HDAC Inhibitors Induce HLA Class I Molecules through the SOX10–IRF1 Axis in Clear Cell Sarcoma Cells

Abstract

Although immune checkpoint inhibitors (ICIs) are an effective treatment for clear cell sarcoma (CCS), a rare melanocytic sarcoma with a poor prognosis, their efficacies are still limited. Therefore, a novel therapeutic strategy is required to improve the efficacy of ICIs. We previously reported that histone deacetylase (HDAC) inhibitors increased melanoma immunogenicity through the SOX10–IRF1 pathway and may improve the efficacy of ICIs for melanoma. We herein demonstrated that the inhibition of HDAC induced the expression of HLA class I molecules through IRF1 in CCS cells, similar to melanoma. The suppression of SOX10 by small interfering RNA (siRNA) induced the expression of HLA class I molecules. In addition, the isoform-specific inhibition of HDAC1/3 induced the expression of another IRF1 downstream molecule, PD-L1 in CCS cells in concert with the suppression of SOX10. Furthermore, the knockdown of IRF1 impaired the induction of PD-L1 expression in CCS cells. Therefore, the inhibition of HDAC1/3 has potential as a novel strategy to increase immunogenicity and as combination therapy with ICIs for CCS and melanoma.

INTRODUCTION

Clear cell sarcoma (CCS) is a soft tissue malignancy with melanocytic features in young adults that has a high incidence of metastasis and a poor prognosis.^1–5) CCS is unresponsive to chemotherapy or radiotherapy^6–8); therefore, the development of novel therapeutic strategies is urgently needed for CCS patients.

Recent cancer treatment has been improved by the development of immune checkpoint inhibitors (ICIs), such as antibodies against PD-1, PD-L1/2, and CTLA-4.^9–11) Clinical trials on ICIs for CCS, including the anti-PD-1 antibody, are ongoing. Patients that respond to ICIs may achieve benefits from their combination with target therapies, such as the multi-receptor tyrosine kinase inhibitor, sunitinib; however, some patients do not respond to ICIs.^12–14) Furthermore, some cancers have intrinsic or acquired resistance to ICIs.^15–18) One of the underlying resistance mechanisms is lower immunogenicity in the cancer cells themselves due to genetic mutations, such as mutations in Janus kinase 1/2 (JAK1/2),¹⁷⁾ which phosphorylate STATs by interferon-γ (IFN-γ) stimuli and induce the expression of IRF1.

IRF1 acts downstream of the IFN-γ–JAK–STAT pathway^19,20) and regulates gene expression not only for antigen-presenting molecules, such as MHC class I, TAP, and β2M, but also immune checkpoint molecules, including PD-L1 and PD-L2.^20,21) Mutations in the IFN-γ–JAK–STAT pathway may reduce the expression of IRF1-dependent immune markers, thereby impairing the cancer-recognition ability of cytotoxic CD8⁺ T cells or leading to a poor response to ICIs in patients. Therefore, it is important to induce IRF1 activity independent of the JAK–STAT pathway. We recently demonstrated that histone deacetylase inhibitors (HDACi) increased melanoma immunogenicity through the SOX10–IRF1 pathway independent of the JAK–STAT pathway.²²⁾ SOX10 is a transcription factor that is expressed in melanoma, regulates the melanoma oncogene MITF, and is also expressed in some CCS.²³⁾ These findings prompted us to examine the effects of HDACi on IRF1 expression in CCS cells.

In the present study, we showed the knockdown of SOX10 and treatment with HDACi induced the expression of HLA class I molecules in CCS cells. By screening some HDACi, we identified HDAC1/3 as important targets for inducing the expression of HLA class I molecules. In addition, the expression of another IRF1 downstream molecule, PD-L1 was increased by the inhibition of HDAC1/3 in CCS cells. Importantly, the induction of PD-L1 by the inhibition of HDAC1/3 was impaired by the knockdown of IRF1, but not by the JAK inhibitor baricitinib. These results suggest that HDACi increase immunogenicity in CCS, similar to melanoma, and may improve the efficacy of ICIs against CCS with low immunogenicity.

MATERIALS AND METHODS

Antibodies and Reagents

The antibody (C-5) against MITF was kindly gifted by Dr. Fisher D.E. (Massachusetts General Hospital, Boston, MA, U.S.A.). SOX10 and β-actin antibodies were obtained from Santa Cruz Biotechnology (Santa Cruz, CA, U.S.A.). The IRF1 antibody were purchased from Cell Signaling Technology (Danvers, MA, U.S.A.). The HDACi used were vorinostat (suberoylanilide hydroxamic acid; Cayman Chemical, Ann Arbor, MI, U.S.A.), TMP269 (Cayman Chemical), ricolinostat (BioVision, Exton, PA, U.S.A.), RGFP109 (MedChemExpress, Monmouth Junction, NJ, U.S.A.), and BRD73954 (Sigma-Aldrich, St. Louis, MO, U.S.A.).

Cell Culture

Hewga-CCS,²⁴⁾ MP-CCS-SY,²⁵⁾ and KAS²⁶⁾ cells were established by Dr. Outani H. (Osaka University Graduate School of Medicine, Japan), Dr. Moritake H. (Miyazaki Medical College, Japan), and Dr. Nakamura T. (Japanese Foundation for Cancer Research, Japan), respectively. SU-CCS-1 and UACC257 were purchased from the American Type Culture Collection (ATCC, Rockville, TX, U.S.A.). Hewga-CCS, MP-CC-S-SY, KAS, and SU-CCS-1 were maintained in Dulbecco’s modified Eagle’s medium (high-glucose; Nissui Pharmaceutical, Tokyo, Japan) supplemented with 10% fetal calf serum, 4 mM L-glutamine, 100 U/mL penicillin, and 100 U/mL streptomycin (Meiji Seika Pharma, Tokyo, Japan) at 37 °C in 5% CO₂. UACC257 cells were maintained in RPMI-1640 (Nissui Pharmaceutical) supplemented with 10% fetal calf serum, 2 mM glutamine, 100 U/mL penicillin, and 100 µg/mL streptomycin at 37 °C in 5% CO₂.

Immunoblotting

Whole cell lysates and nuclear extracts were prepared as previously described,²²⁾ resolved by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE), and transferred to an Immobilon-P nylon membrane (Merk KGaA). The membrane was treated with Block Ace (KAC, Hyogo, Japan) and incubated with the primary antibodies described above. Antibodies were detected using horseradish peroxidase-conjugated anti-rabbit or mouse immunoglobulin G (Dako, Agilent Technologies, Santa Clara, CA, U.S.A.) and visualized with an enhanced chemiluminescence system (Thermo Fisher Scientific). Some antibody reactions were performed in Can Get Signal solution (Toyobo, Osaka, Japan).

RNA Interference

Small interfering RNAs (siRNAs) for SOX10 (s13309 and s13310, Thermo Fisher Scientific, Rockford, IL, U.S.A.), IRF1 (s7503, Thermo Fisher Scientific), and negative control #1 (Thermo Fisher Scientific) were used for transfection at a final concentration of 12.5 nM of cancer cells by Lipofectamine RNAiMAX reagent (Thermo Fisher Scientific). Cells were used in experiments 48 h post-transfection.

Flow Cytometry

Cells were treated with each HDACi for 24 h. In siRNA transfection, cells were reverse-transfected with 12.5 nM siRNA for 48 h as described above and treated with each HDACi for 24 h. After their treatment, cells were stained with a PE-conjugated human CD274 or fluorescein isothiocyanate (FITC)-conjugated anti-human HLA-A/B/C antibody (eBioscience). All flow cytometry data were analyzed using FlowJo software (TreeStar Software). Relative mean fluorescent intensities were normalized by each control value.

Statistical Analysis

Significance was calculated using Graphpad Prism software (GraphPad Software, Inc., San Diego, CA, U.S.A.). More than three means were compared using a two- or one-way ANOVA with the Bonferroni correction, and two means were compared using the unpaired Student’s t-test. p < 0.05 was considered to be significant.

RESULTS

SOX10 Suppression Induces HLA Class I Expression in CCS

CCS is pathologically similar to melanoma, which contains melanin particles.^1–5) The expression of melanin synthesis-related enzymes is transcriptionally regulated by two transcription factors, SOX10 and the melanocyte-specific isoform of MITF.^27–32) We identified the expression of SOX10 and MITF in all of the human CCS cell lines tested as well as in UACC257 human melanoma cells (Fig. 1A). Although SOX10 was expressed in CCS cells, this result does not support the function of SOX10 in CCS being similar to that in melanoma. To elucidate the significance of SOX10 in the regulation of HLA class I molecules, SOX10 was knocked down in the CCS cell lines, Hewga-CCS and MP-CCS-SY (Fig. 1B). Similar to melanoma, the knockdown of SOX10 induced the expression of IRF1, which is the gene responsible for the expression of HLA class I molecules in concert with a reduction in MITF, a SOX10 target gene. The regulation of IRF1 by SOX10 in CCS was also supported by the negative correlation between the expression levels of MITF, a SOX10 functional marker, and IRF1 in CCS (Fig. 1A). In addition to the induction of IRF1, the knockdown of SOX10 in Hewga-CCS and MP-CCS-SY cells up-regulated the cell surface expression of HLA-A/B/C (Figs. 1C, 1D), suggesting the regulation of HLA class I molecules by SOX10 in CCS.

Fig. 1. SOX10 Negatively Regulates the Expression of IRF1 and HLA Class I Molecules in Clear Cell Sarcoma

(A) The expression of SOX10 and MITF in clear cell sarcoma cells was assessed by Western blotting. (B–D) Hewga-CCS and MP-CCS-SY cells transfected with siCNTL or siSOX10 (#9 or #10) for 48 h were subjected to Western blotting (B) or flow cytometry (C, D). Representative flow cytometry graphs are shown (C). The relative mean fluorescent intensities are normalized to that of siCNTL-transfected cells, and are presented as the mean ± S.D. of at least three independent experiments (D). * p < 0.05 vs. mean fluorescent intensity in each siCNTL-transfected cells by one-way ANOVA followed by the Bonferroni post test.

Various HDACi Induce HLA Class I Molecules in CCS Cells

Since HDACi suppress the expression of SOX10 in melanoma and CCS,³³⁾ the effects of various HDACi with different specificities on HLA class I molecules were examined in Hewga-CCS cells. As shown in Fig. 2, vorinostat (inhibiting HDAC1 to 11), ricolinostat (inhibiting HDAC1, 2, 3, 6, and 8), and RGFP109 (inhibiting HDAC1 and 3) significantly induced the cell surface expression of HLA-A/B/C (Figs. 2A, 2C), whereas TMP268 (inhibiting HDAC4, 5, 7, and 9) and BRD73954 (inhibiting HDAC6 and 8) did not (Figs. 2B, 2C). These results suggest the significant role of HDAC1/3 in the induction of HLA class I molecules.

Fig. 2. HDAC1/3 Inhibition Induces the Expression of HLA Class I Molecules in Hewga-CCS Cells

(A) Hewga-CCS cells were treated with each HDAC inhibitor, vorinostat (2 µM), ricolinostat (10 µM), or RGFP109 (10 µM) for 24 h and then subjected to flow cytometry. Representative flow cytometry graphs are shown. (B) Hewga-CCS cells were treated with TMP269 (10 µM) and BRD73954 (10 µM). Other conditions were similar to those in Fig. 2A. (C) The relative mean fluorescent intensities are normalized to that of DMSO-treated cells, and are presented as the mean ± S.D. of at least three independent experiments (D). * p < 0.05 vs. mean fluorescent intensity in DMSO-treated cells by one-way ANOVA followed by the Bonferroni post test.

HDAC1/3 Inhibition Induces the Expression of HLA Class I Molecules and PD-L1 through IRF1 in CCS Cells

Since not only HLA class I molecules, but also PD-L1 have been identified as IRF1 downstream genes,²⁰⁾ we investigated the cell surface expression of PD-L1 with the inhibition of HDAC1/3 in CCS cell lines. In addition to the induced expression of HLA class I molecules, the significant induced cell surface expression of PD-L1 with RGFP109 was detected in all CCS cells examined (Figs. 3A, 3B). These results suggest the involvement of IRF1 in the induction of HLA class I molecules as well as PD-L1 after the inhibition of HDAC1/3 in most CCS cells.

Fig. 3. HDAC1/3 Inhibition Induces the Expression of PD-L1 and HLA Class I Molecules in Various Clear Cell Sarcomas

(A) Each clear cell sarcoma cell line was treated with RGFP109 (10 µM) for 24 h and then subjected to flow cytometry. Representative flow cytometry graphs are shown. (B) The relative mean fluorescent intensities are normalized to that of DMSO-treated cells, and are presented as the mean ± S.D. of at least three independent experiments. * p < 0.05 vs. mean fluorescent intensity in DMSO-treated cells by two-way ANOVA followed by the Bonferroni post test.

HDAC1/3 Inhibition Induces IRF1 Expression in Concert with a Reduction in SOX10 Expression

We next examined the effects of HDAC1/3 inhibition on the expression of IRF1. Following chemical inhibition by RGFP109, the reduction in the expression of SOX10 and the induction of IRF1 expression occurred in a dose-dependent manner in Hewga-CCS and MP-CCS-SY cells in concert with the suppression of SOX10 and MITF (Fig. 4A, Supplementary Fig. S1A). To further clarify the significance of IRF1 after the inhibition of HDAC1/3, we examined the cell surface expression of PD-L1 after the RGFP109 treatment with siRNA for IRF1 because of the stronger induction of PD-L1 than HLA class I molecules in Hewga-CCS cells (Fig. 3). The RGFP109-induced cell surface expression of PD-L1 was impaired by the knockdown of IRF1 (Fig. 4B). On the other hand, a JAK inhibitor, baricitinib, could not inhibit the RGFP109-induced cell surface expression of PD-L1 (Fig. 4C), which supports the induction of IRF1 by HDAC inhibition in a JAK-independent manner, although IFN-γ-induced PD-L1 expression was completely impaired by baricitinib (Fig. 4D). We also confirmed the similar results in MP-CCS-SY cells (Supplementary Fig. S1). These results suggest that HDAC1/3 inhibition regulated IRF1 targets through the induction of IRF1 expression in a JAK-independent manner.

Fig. 4. IRF1 Is Indispensable for the Induction of PD-L1 Expression by HDAC1/3 Inhibition

(A) Hewga-CCS cells were treated with RGFP109 at the indicated dose for 24 h and then subjected to Western blotting. (B) Hewga-CCS cells were transfected with siCNTL or siIRF1 for 24 h. Cells were then treated with RGFP109 (10 µM) for 24 h and subjected to flow cytometry. Representative flow cytometry graphs are shown (left panel). The relative mean fluorescent intensities are normalized to that of DMSO-treated cells, and are presented as the mean ± S.D. of at least three independent experiments (right panel). * p < 0.05 vs. mean fluorescent intensity in DMSO-treated cells by one-way ANOVA followed by the Bonferroni post test. (C, D) Hewga-CCS cells were pretreated with baricitinib (0.5 µM) for 30 min and then treated with RGFP109 (10 µM) for 24 h (C) or IFN-γ for 24 h (D). Cells were subjected to flow cytometry. Representative flow cytometry graphs are shown (left panel) and the relative mean fluorescent intensities are shown (right panel). Other conditions were similar to those in Fig. 4B.

DISCUSSION

In the present study, we identified SOX10 as a regulator of HLA class I molecules in CCS cells. In addition, HDACi induced the expression of HLA class I molecules through the SOX10–IRF1 pathway. Regarding the clinical relevance of the present results, HDACi may change the CCS microenvironment and concurrently increase the efficacy of ICIs by enhancing CCS immunogenicity through the induction of HLA and PD-L1.

Since CCS is often described as a malignant melanoma of soft tissues, some of its characteristics are common to those of melanoma, such as melanin production and the expression of the melanocyte-specific isoform of MITF.^1–5) Although the expression of the transcription factor SOX10 was previously shown to be similar in CCS and melanoma,²³⁾ it remains unclear whether SOX10 suppression exerts similar pathological effects in CCS as those in melanoma. Consistent with melanoma, we detected a reduction in MITF in CCS (Fig. 1B) as well as the induction of IRF1 and its downstream targets, HLA class I molecules and PD-L1, after SOX10 suppression by siRNA or HDAC inhibition (Figs. 1B, 3). Although we did not show the data about the mechanism in which SOX10 suppression induces IRF1 expression in CCS cells, its IRF1 induction could be mediated through IRF4 reduction as we previously described in melanoma.²²⁾ These results suggest a similar SOX10 function between melanoma and CCS.

We demonstrated that HDACi induced the expression of HLA class I molecules and it has been demonstrated that HDACi suppressed another oncogenic fusion protein, EWSR1-ATF1, in CCS by inhibiting SOX10.³⁴⁾ Since both SOX10 and EWSR1-ATF1 directly regulates the oncogene MITF,²³⁾ the pan-HDACi, vorinostat, has been suggested to inhibit the growth of CCS in vivo.³⁴⁾ Based on the results showing the induction of HLA class I molecules by HDACi in the present study, the suppression of SOX10 by HDACi may serve dual purposes by inhibiting tumor growth through the expression of MITF and EWSR1-ATF1, and by inducing anti-tumor immunity through HLA class I molecules. Moreover, we showed that HDACi induced the expression of PD-L1 in a JAK-independent manner in CCS (Fig. 4, Supplementary Fig. S1), which is consistent with previous findings in melanoma.²²⁾ Although there is currently no information on JAK1/2 mutations in CCS, the present results imply that the suppression of SOX10 by HDACi may be useful for CCS patients, even those with resistance to ICIs caused by JAK1/2 mutations.

HDACi have potential as a treatment for CCS; however, there are some obstacles due to their specificity. The clinically available HDACi, vorinostat, for cutaneous T-cell lymphoma has a broad spectrum for various HDAC isoforms.³⁵⁾ Besides the specificities of HDACi to HDAC isoforms, acetylation activities against proteins other than histones have been reported. Given the lower specificities of HDACi, it is essential to identify their specific isoforms at least to regulate the expression of SOX10 in CCS. In this context, we showed that the inhibition of HDAC1/3 induced the expression of HLA class I molecules through the SOX10–IRF1 pathway in CCS (Fig. 2); however, further studies are needed to clarify the relationship between HDAC1/3 and SOX10. In clinical settings, currently available HDACi demonstrate superior efficacy with a low incidence of adverse effects,³⁶⁾ and grade 3–4 immune-related adverse events associated with ICIs are generally manageable with glucocorticoid treatment over the course of several weeks.³⁷⁾ Furthermore, the induction of HLA class I molecules by HDACi in this study may be restricted to cells expressing SOX10, implying little effects on various tissues. Therefore, pan-HDACi might still have potential as an adjuvant to support increases in tumor immunogenicity by ICIs with permissible and controllable adverse effects. Although the effects of HDACi in combination with ICIs on human CCS cell lines in vivo or in vitro have not been definitively confirmed so far, there may be similar effects observed in CCS as seen in a mouse melanoma model in vivo.²²⁾ Collectively, the present results demonstrated that the specific inhibition of HDAC1/3 was sufficient to induce the expression of HLA class I molecules in CCS. Therefore, the inhibition of HDAC1/3 in CCS may increase immunogenicity and achieve better clinical benefits with ICIs for CCS.

Acknowledgments

We thank members of the Sakurai Laboratory for their discussions and suggestions. This work was supported in part by JSPS KAKENHI Grant Numbers: 18K07227 (S.Y.), 24K10355 (S.Y.), and 23K24026 (H.S.), and research Grants from Takeda Science Foundation (S.Y.) and GSK Japan Research Grant 2021 (S.Y.).

Conflict of Interest

The authors declare no conflict of interest.

Supplementary Materials

This article contains supplementary materials.

REFERENCES

• 1) Swanson PE, Wick MR. Clear cell sarcoma. An immunohistochemical analysis of six cases and comparison with other epithelioid neoplasms of soft tissue. Arch. Pathol. Lab. Med., 113, 55–60 (1989).
• 2) Chung EB, Enzinger FM. Malignant melanoma of soft parts: a reassessment of clear cell sarcoma. Am. J. Surg. Pathol., 7, 405–414 (1983).
• 3) Granter SR, Weilbaecher KN, Quigley C, Fletcher CD, Fisher DE. Clear cell sarcoma shows immunoreactivity for microphthalmia transcription factor: further evidence for melanocytic differentiation. Mod. Pathol., 14, 6–9 (2001).
• 4) Antonescu CR, Tschernyavsky SJ, Woodruff JM, Jungbluth AA, Brennan MF, Ladanyi M. Molecular diagnosis of clear cell sarcoma: detection of EWS-ATF1 and MITF-M transcripts and histopathological and ultrastructural analysis of 12 cases. J. Mol. Diagn., 4, 44–52 (2002).
• 5) Enzinger FM. Clear-cell sarcoma of tendons and aponeuroses: an analysis of 21 cases. Cancer, 18, 1163–1174 (1965).
• 6) Deenik W, Mooi WJ, Rutgers EJ, Peterse JL, Hart AA, Kroon BB. Clear cell sarcoma (malignant melanoma) of soft parts: a clinicopathologic study of 30 cases. Cancer, 86, 969–975 (1999).
• 7) Finley JW, Hanypsiak B, McGrath B, Kraybill W, Gibbs JF. Clear cell sarcoma: the Roswell Park experience. J. Surg. Oncol., 77, 16–20 (2001).
• 8) Ferrari A, Casanova M, Bisogno G, Mattke A, Meazza C, Gandola L, Sotti G, Cecchetto G, Harms D, Koscielniak E, Treuner J, Carli M. Clear cell sarcoma of tendons and aponeuroses in pediatric patients: a report from the Italian and German Soft Tissue Sarcoma Cooperative Group. Cancer, 94, 3269–3276 (2002).
• 9) Hodi FS, O’Day SJ, McDermott DF, et al. Improved survival with ipilimumab in patients with metastatic melanoma. N. Engl. J. Med., 363, 711–723 (2010).
• 10) Topalian SL, Hodi FS, Brahmer JR, et al. Safety, activity, and immune correlates of anti-PD-1 antibody in cancer. N. Engl. J. Med., 366, 2443–2454 (2012).
• 11) Brahmer JR, Tykodi SS, Chow LQ, et al. Safety and activity of anti-PD-L1 antibody in patients with advanced cancer. N. Engl. J. Med., 366, 2455–2465 (2012).
• 12) Tazzari M, Palassini E, Vergani B, Villa A, Rini F, Negri T, Colombo C, Crippa F, Morosi C, Casali PG, Pilotti S, Stacchiotti S, Rivoltini L, Castelli C. Melan-A/MART-1 immunity in a EWS-ATF1 translocated clear cell sarcoma patient treated with sunitinib: a case report. BMC Cancer, 15, 58 (2015).
• 13) Marcrom S, De Los Santos JF, Conry RM. Complete response of mediastinal clear cell sarcoma to pembrolizumab with radiotherapy. Clin. Sarcoma Res., 7, 14 (2017).
• 14) Martin-Broto J, Hindi N, Grignani G, Martinez-Trufero J, Redondo A, Valverde C, Stacchiotti S, Lopez-Pousa A, D’Ambrosio L, Gutierrez A, Perez-Vega H, Encinas-Tobajas V, de Alava E, Collini P, Pena-Chilet M, Dopazo J, Carrasco-Garcia I, Lopez-Alvarez M, Moura DS, Lopez-Martin JA. Nivolumab and sunitinib combination in advanced soft tissue sarcomas: a multicenter, single-arm, phase Ib/II trial. J. Immunother. Cancer, 8, e001561 (2020).
• 15) Zaretsky JM, Garcia-Diaz A, Shin DS, et al. Mutations Associated with acquired resistance to PD-1 blockade in melanoma. N. Engl. J. Med., 375, 819–829 (2016).
• 16) Gao J, Shi LZ, Zhao H, Chen J, Xiong L, He Q, Chen T, Roszik J, Bernatchez C, Woodman SE, Chen PL, Hwu P, Allison JP, Futreal A, Wargo JA, Sharma P. Loss of IFN-gamma pathway genes in tumor cells as a mechanism of resistance to anti-CTLA-4 therapy. Cell, 167, 397–404.e9 (2016).
• 17) Shin DS, Zaretsky JM, Escuin-Ordinas H, et al. Primary resistance to PD-1 blockade mediated by JAK1/2 mutations. Cancer Discov., 7, 188–201 (2017).
• 18) Hellmann MD, Nathanson T, Rizvi H, et al. Genomic features of response to combination immunotherapy in patients with advanced non-small-cell lung cancer. Cancer Cell, 33, 843–852.e4 (2018).
• 19) Platanias LC. Mechanisms of type-I- and type-II-interferon-mediated signalling. Nat. Rev. Immunol., 5, 375–386 (2005).
• 20) Garcia-Diaz A, Shin DS, Moreno BH, Saco J, Escuin-Ordinas H, Rodriguez GA, Zaretsky JM, Sun L, Hugo W, Wang X, Parisi G, Saus CP, Torrejon DY, Graeber TG, Comin-Anduix B, Hu-Lieskovan S, Damoiseaux R, Lo RS, Ribas A. Interferon receptor signaling pathways regulating PD-L1 and PD-L2 expression. Cell Rep., 19, 1189–1201 (2017).
• 21) Girdlestone J, Isamat M, Gewert D, Milstein C. Transcriptional regulation of HLA-A and -B: differential binding of members of the Rel and IRF families of transcription factors. Proc. Natl. Acad. Sci. U.S.A., 90, 11568–11572 (1993).
• 22) Yokoyama S, Takahashi A, Kikuchi R, Nishibu S, Lo JA, Hejna M, Moon WM, Kato S, Zhou Y, Hodi FS, Song JS, Sakurai H, Fisher DE, Hayakawa Y. SOX10 regulates melanoma immunogenicity through an IRF4-IRF1 axis. Cancer Res., 81, 6131–6141 (2021).
• 23) Davis IJ, Kim JJ, Ozsolak F, Widlund HR, Rozenblatt-Rosen O, Granter SR, Du J, Fletcher JA, Denny CT, Lessnick SL, Linehan WM, Kung AL, Fisher DE. Oncogenic MITF dysregulation in clear cell sarcoma: defining the MiT family of human cancers. Cancer Cell, 9, 473–484 (2006).
• 24) Outani H, Tanaka T, Wakamatsu T, Imura Y, Hamada K, Araki N, Itoh K, Yoshikawa H, Naka N. Establishment of a novel clear cell sarcoma cell line (Hewga-CCS), and investigation of the antitumor effects of pazopanib on Hewga-CCS. BMC Cancer, 14, 455 (2014).
• 25) Moritake H, Sugimoto T, Asada Y, Yoshida MA, Maehara Y, Epstein AL, Kuroda H. Newly established clear cell sarcoma (malignant melanoma of soft parts) cell line expressing melanoma-associated Melan-A antigen and overexpressing C-MYC oncogene. Cancer Genet. Cytogenet., 135, 48–56 (2002).
• 26) Jishage M, Fujino T, Yamazaki Y, Kuroda H, Nakamura T. Identification of target genes for EWS/ATF-1 chimeric transcription factor. Oncogene, 22, 41–49 (2003).
• 27) Yavuzer U, Keenan E, Lowings P, Vachtenheim J, Currie G, Goding CR. The microphthalmia gene product interacts with the retinoblastoma protein in vitro and is a target for deregulation of melanocyte-specific transcription. Oncogene, 10, 123–134 (1995).
• 28) Bentley NJ, Eisen T, Goding CR. Melanocyte-specific expression of the human tyrosinase promoter: activation by the microphthalmia gene product and role of the initiator. Mol. Cell. Biol., 14, 7996–8006 (1994).
• 29) Yasumoto K, Yokoyama K, Shibata K, Tomita Y, Shibahara S. Microphthalmia-associated transcription factor as a regulator for melanocyte-specific transcription of the human tyrosinase gene. Mol. Cell. Biol., 14, 8058–8070 (1994).
• 30) Opdecamp K, Nakayama A, Nguyen MT, Hodgkinson CA, Pavan WJ, Arnheiter H. Melanocyte development in vivo and in neural crest cell cultures: crucial dependence on the Mitf basic-helix-loop-helix-zipper transcription factor. Development, 124, 2377–2386 (1997).
• 31) Huber WE, Price ER, Widlund HR, Du J, Davis IJ, Wegner M, Fisher DE. A tissue-restricted cAMP transcriptional response: SOX10 modulates alpha-melanocyte-stimulating hormone-triggered expression of microphthalmia-associated transcription factor in melanocytes. J. Biol. Chem., 278, 45224–45230 (2003).
• 32) Ludwig A, Rehberg S, Wegner M. Melanocyte-specific expression of dopachrome tautomerase is dependent on synergistic gene activation by the Sox10 and Mitf transcription factors. FEBS Lett., 556, 236–244 (2004).
• 33) Yokoyama S, Feige E, Poling LL, Levy C, Widlund HR, Khaled M, Kung AL, Fisher DE. Pharmacologic suppression of MITF expression via HDAC inhibitors in the melanocyte lineage. Pigment Cell Melanoma Res., 21, 457–463 (2008).
• 34) Mae H, Outani H, Imura Y, Chijimatsu R, Inoue A, Kotani Y, Yasuda N, Nakai S, Nakai T, Takenaka S, Okada S. Targeting the clear cell sarcoma oncogenic driver fusion gene EWSR1::ATF1 by HDAC inhibition. Cancer Res. Commun., 3, 1152–1165 (2023).
• 35) Mann BS, Johnson JR, Cohen MH, Justice R, Pazdur R. FDA approval summary: vorinostat for treatment of advanced primary cutaneous T-cell lymphoma. Oncologist, 12, 1247–1252 (2007).
• 36) Gao X, Shen L, Li X, Liu J. Efficacy and toxicity of histone deacetylase inhibitors in relapsed/refractory multiple myeloma: Systematic review and meta-analysis of clinical trials. Exp. Ther. Med., 18, 1057–1068 (2019).
• 37) Conroy M, Naidoo J. Immune-related adverse events and the balancing act of immunotherapy. Nat. Commun., 13, 392 (2022).