The Alteration of Endogeneous Keratin Networks after Transfection of Hair Keratin Genes

Abstract

To define the interactions reguired for the filament assembly of differentiation-specific keratins, active copies of mouse hair keratin mHa 1 and mHb 4 genes were introduced into a rat kangaroo kidney epitherial cell line (PtK 2) and a rat stratified squamous epitherial cell line (rat epidermal keratinocyte). In PtK2 transient transfectants, when introduced individually or in combination, mHa 1 and mHb 4 formed aggregates of ring-like structures of various sizes at the perinuclear region with no evidence of organization into a keratin network. These aggregates altered the distribution of the endogeneous keratins and vimentin. In most of the cells carrying the ring-like structures of mHa 1 and mHb 4 around their nuclei, the endogenous keratin network collapsed and localized around the nucleus. Furthermore, the densely accumulated endogenous keratin surrounded the ring-like aggregates with partial co-localization. However, when transfected into the rat epidermal keratinocytes, mHa 1 and mHb 4 were able to co-localize with the well-developed cytoskeleton of endogenous keratins. These results showed that, in constrast to keratin pairs K5/K14and K8/K18, the mHa 1/mHb 4 pair is unable to develop an extensive keratin network on its own, and that there are possible defferential abilities among these hair keratins and other keratins to form well-developed cytoplasmic networks.