SQUAMOUS CARCINOMA CELL-LINES FAIL TO RESPOND TO 1,25-DIHYDROXYVITAMIN-D DESPITE NORMAL LEVELS OF THE VITAMIN-D-RECEPTOR

Squamous carcinoma cells (SCC) fail to differentiate under conditions that are favorable for the growth and differentiation of normal human keratinocytes. Human keratinocytes differentiate from a highly prolife rative basal cell to a terminally differentiated cornified cell in cul ture in the presence of physiological levels of extracellular calcium, 1,25-Dihydroxyvitamin D (1,25[OH]D-2(3)) potentiates this process, Pr evious studies have shown that the differentiation process in keratino cytes is associated with increased expression of the genes for involuc rin and transglutaminase, the products of which participate in cornifi ed envelope formation, The mRNA for involucrin and transglutaminase wa s not detected in the SCC lines studied (viz,, SCC4, 12B2, 12F2, A431, and HACAT) when they were grown in serum free medium, Addition of at least 2% fetal bovine serum for 48 h triggered the expression of these genes, which could then be maintained in the absence of serum, Serum was not required for induction of these genes in keratinocytes. In the se cells, 1,25(OH)(2)D-3 stimulated the expression of involucrin and t ransglutaminase in a concentration-dependent manner, while the SCC lin es failed to respond to 1,25(OH)(2)D-3 regardless of whether these cel ls had been pre-exposed to serum, An important factor that mediates 1, 25(OH)(2)D-3-stimulated gene expression is the vitamin D receptor, but vitamin D receptor mRNA levels in all the SCC lines examined were com parable to those in keratinocytes. Furthermore, the vitamin D receptor protein levels in SCC lines as assessed by ligand-binding analysis we re comparable to those of keratinocytes. Thus, the mediators of 1,25(O H)(2)D-3 action on gene expression other than the vitamin D receptor m ay be missing or defective in SCC lines, whereas the mediators of as y et undefined agents in serum may be better expressed in SCC lines than in keratinocytes. Our results indicate that, although SCC lines are c apable of expressing the genes for the proteins involved in differenti ation, the control of the expression of these genes by 1,25(OH)(2)D-3 is abnormal in SCC despite the presence of a functional vitamin D rece ptor in concentrations equivalent to those in keratinocytes.