Role for Protein Kinase C-α in Keratinocyte Growth Arrest

Abstract

Multiple protein kinase C (PKC) isoforms have been associated with the epidermal keratinocyte (KC) granular layer differentiation program. Here we show PKCalpha membrane localization and substrate phosphorylation in the first suprabasal KCs of normal human epidermis, suggesting activation in vivo in the lower spinous layers where terminal differentiation-associated growth arrest occurs. To determine if PKCalpha is sufficient for KC growth arrest, we expressed a constitutively active PKCalpha (PKCalpha Delta22-28) in normal human KCs and observed growth arrest and accumulation of cells in G1. PKCalpha Delta22-28 inhibited DNA synthesis through the induction of the cyclin-dependent kinase inhibitor p21. Furthermore, downregulation of PKCalpha in an in vitro organotypic epidermis resulted in increased basal and suprabasal proliferation marker expression, decreased differentiation, and reduced epidermal stratification. Together these results indicate that PKCalpha activation is both necessary and sufficient to trigger irreversible growth arrest during human KC differentiation.

Lipin-1 expression is critical for keratinocyte differentiation

“…In our study, inhibition of lipin-1 expression by targeting which is accompanied by the induction of p21 in normal keratinocytes ( 49,50 ). Consistent with TPA treatment, overexpression of PKC ␦ and -␣ in keratinocytes prevents proliferation by a mechanism associated with elevated p21 expression ( 38,39 ). On the contrary, we found that lipin-1 KD-induced suppression and lipin-1-induced activation of PKC ␣ are associated with induction and inhibition of p21 expression, respectively, in NHEKs ( Fig.…”

“…In this study, we show that PKC ␣ activation is regulated by lipin-1 in NHEKs. PKC ␣ is expressed and activated in the fi rst basal or lower spinous layers in human epidermis ( 39 ). These results suggest that lipin-1 may be involved in PKC ␣ activation in the basal and spinous layers the fi nal reaction in TAG synthesis die shortly after birth due to abnormal energy metabolism and impaired skin permeability barrier function ( 46 ).…”

“…6 ), while PKC ␣ overexpression transiently induced PKC ␣ and p21 expression ( 39 ). Therefore, the discrepancy of the effect of PKC ␣ activation/inhibition on p21 may be attributed to differences in duration/magnitude of stimuli.…”

“…2). PKC activation by DAG controls the proliferation of keratinocytes ( 38,39 ). To assess whether altered DAG contents led to impaired PKC activation, we assessed the phosphorylation of PKC substrates.…”

The Effect of Pantothenic Acid Deficiency on Keratinocyte Proliferation and the Synthesis of Keratinocyte Growth Factor and Collagen in Fibroblasts

“…The low proliferative ability and enhanced differentiation of keratinocytes cultured in pantothenic acid-deficient DMEM indicate that the depletion of pantothenic acid may decelerate or arrest the cell cycle, thus enhancing keratinocyte differentiation (9). It is known that the balance between proliferation and differentiation is regulated by various factors, and protein kinase C or tyrosine kinase may be involved in the "switch" from proliferation to differentiation (10), although the detailed mechanism has not been reported. Moreover, it has been shown that an increased intracellular Ca 2+ concentration or high cell density might induce cell differentiation (11).…”