The role of the cell attachment in the regulation of telomerase during keratinocyte differentiation

Abstract

The catalytic subunit of telomerase TERT has non-canonical functions, which are independent of telomere elongation and sometimes telomerase activity. In skin keratinocytes, both TERT expression and anoikis are regulated by extracellular matrix molecules and their integrin receptors, but the effect of TERT deregulation on anoikis has not been previously investigated. HaCaT cells expressing wild-type TERT, TERT-HA (non-canonical function only) DnTERT (catalytically inactive TERT) and the empty vector (PURO) were created by retroviral transduction. HaCaT anoikis was monitored after disengagement of integrins following anchorage deprivation by nuclear staining and FACS. The expression of both TERT and TERT-HA, and to a lesser extent DnTERT, significantly decreased the appearance of apoptotic HaCaT cells in suspension. This showed that TERT could mute anoikis even in the absence of telomere lengthening but that it may require telomerase activity for optimum effect. TERT/TERT-HA did not mute cisplatin-induced HaCaT apoptosis, suggesting that the effects are specific to anoikis. Telomerase activity in the anchorage-deprived samples significantly decreased compared to the controls at time zero in all the samples. hTERT mRNA expression dropped in all groups in suspension compared to the zero time empty vector controls but the expression was still higher in those cells over expressing TERT/TERT-HA than the controls at zero time, suggesting a relationship between TERT/TERT-HA expression and resistance to anoikis. However, TERC expression increased in suspension similarly in all experimental groups. Therefore, these results suggest that the downregulation of TERT and not TERC contributes to the downregulation of telomerase in suspension, although the downregulation of ectopically expressed TERT also suggests that post-transcriptional mechanisms are involved. TERT splice variants were rare and not strikingly regulated in suspended keratinocytes. Western blot and FACS analyses indicated that TERT does not act by affecting integrin expression or their density on the keratinocyte surface, suggesting a point of action downstream of integrins