Possible Factors Related to Phenotype Change from Adenocarcinoma to Squamous Cell Carcinoma

Abstract

Squamous differentiation/squamous metaplasia is a common feature associated with lung and endometrial adenocarcinomas, but is very rare in the case of colonic and gastric adenocarcinomas. Cases of squamous cell carcinoma and adenosquamous carcinoma (criteria of the Japan Lung Cancer Society) of the lung and endometrial adenocarcinoma with squamous differentiation infected with human papillomavirus (HPV) are frequently seen in Okinawa. A correlation between squamous differentiation and HPV infection was demonstrated (p<0.05) [11, 31], and the squamous cell carcinoma components are HPV-positive by in situ hybridization method. The adenocarcinoma cells adjacent to the squamous cell carcinoma components are enlarged, and are also positive for HPV. The production of high molecular weight keratin (HMK) (Moll's No. 1, 5, 10, and 14) [1, 14] and involucrin is induced in the squamous cell carcinoma component and also in adjacent enlarged cells. Further, in Okinawa, squamous metaplasia of the bronchial epithelium are occasionally positive for HPV by in situ hybridization. We postulated that HPV causes phenotype change/squamous metaplasia. We then transfected human papillomavirus 6, 16 and 18 in plasmid pBR322 into cultured adenocarcinoma cells (DLD-1 [4] and PC-14 cells) [13, 16]. DLD-1 cells were the cultured human intestinal adenocarcinoma (moderately differentiated), and PC-14 cells were cultured human lung adenocarcinoma. In our experiments, we chose these two cultured adenocarcinoma cells for following reasons. Squamous differentiation is frequently observed in the case of lung carcinomas, but rare in colonic carcinomas. We used one each of the cultured adenocarcinoma cell lines from both groups. Further, to investigate the effects of HPV transfection on apoptosis and inhibition of the growth, p53 gene mutated (inactivated) carcinoma cells [20, 34] were used. The phenotype change/squamous metaplasia was observed, and was apparent in the case of HPV 16 transfected DLD-1 cells, although in the case of human intestinal adenocarcinoma, squamous differentiation was very rare. It was considered that squamous differentiation was induced by HPV transfection regardless of the tissue type [13]. For this reason, in this report we consider HPV 16 transfected DLD-1 cells. Immunohistochemically HMK (Moll's No. 1, 5, 10 and 14) [1, 15] and involucrin [35] were strongly demonstrated in the cytoplasm of HPV transfected cells. Further, the transglutaminase I [6] and involucrin mRNA were also detected by use of RT-PCR. The growth of the HPV transfected cells was reduced, and the population of G0-G1 phase cells increased. The expression levels of the cell cycle related molecules, cdk2 and cyclin D3 decreased. On the other hand, the proportion of apoptotic cells increased, and the expression level of DNase γ also increased markedly [13].
Although the HPV E6-p53 and E7-Rb interactions have been well known, transcriptional trans-activity of HPV for other cellular genes, for example, cytokeratin and cell cycle associated genes, might be considered [13, 33].