SUMMARY:Keratins are intermediate filament proteins whose expression in epithelial tissues is closely linked to their differentiated state. The greatest complexity of this expression is seen in the epidermis and associated structures. The critical basal (proliferative) cell layer expresses the major keratin pair, K5 and K14, but it also expresses an additional type I keratin, K15, about which far less is known. We have compared the expression of K15 with K14 in normal, pathological, and tissue culture contexts; distinct differences in their expression patterns have been observed that imply different regulation and function for these two genes. K15 appears to be preferentially expressed in stable or slowly turning over basal cells. In steady-state epidermis, K15 is present in higher amounts in basal cells of thin skin but in lower amounts in the rapidly turning over thick plantar skin. Although remaining high in basal cell carcinomas (noninvasive) it is suppressed in squamous cell carcinomas (which frequently metastasize). Wounding-stimulated epidermis loses K15 expression, whereas K14 is unchanged. In cultured keratinocytes, K15 levels are suppressed until the culture stratifies, whereas K14 is constitutively expressed throughout. Therefore, unlike K14, which appears to be a fundamental component of all keratinocytes, K15 expression appears to be more tightly coupled to a mature basal keratinocyte phenotype. (Lab Invest 2000, 80:1701-1710.

Monoclonal antibodies raised to a number of microfilament-associated proteins were shown to recognize the appropriate proteins in extracts from human colon tissue. They were then used in an immunohistochemical study of normal colonic mucosa, adenomas, and adenocarcinomas. A strong reaction was seen in stromal cells within the tumours (both adenomas and adenocarcinomas) when frozen sections were stained with antibodies to filamin and caldesmon. In addition, a similar reaction was seen in the adenocarcinomas when stained with antibodies to talin and gelsolin. We believe that immunohistochemical staining with these antibodies reveals a tumour-induced process in the surrounding cells, possibly related to a host response to tumours.