RasGRP1 represents a novel non-protein kinase C phorbol ester signaling pathway in mouse epidermal keratinocytes.
The mouse skin model of carcinogenesis has been instrumental in our appreciation of the multistage nature of carcinogenesis. In this system, tumor promotion is a critical step in the generation of tumors and is usually achieved by treatment with the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Although it is generally assumed that protein kinase C (PKC) is the sole receptor for TPA in this system, we sought to evaluate whether non-PKC pathways could also contribute to the effects of phorbol esters in skin. We documented expression of the high affinity non-PKC phorbol ester receptor and Ras activator RasGRP1 in mouse primary keratinocytes. Overexpression of RasGRP1 in keratinocytes increased the level of active GTP-loaded Ras. TPA treatment further elevated this Ras activation in a PKC-independent manner and induced the translocation and down-regulation of RasGRP1. Overexpression of RasGRP1 in keratinocytes also caused apoptosis. Finally, induction of keratinocyte differentiation by elevation of extracellular calcium suppressed expression of endogenous RasGRP1, whereas overexpression of RasGRP1 inhibited expression of the differentiation markers keratins 1 and 10 induced by high calcium in the medium. Taken together, our results demonstrate that RasGRP1 is an additional diacylglycerol/phorbol ester receptor in epidermal keratinocytes and suggest that activation of this novel receptor may contribute to some of the phorbol ester- and Ras-mediated effects in mouse epidermis.
Rambaratsingh
Reshmi A
RA
Natural Products Program, Cancer Research Center of Hawaii, Honolulu, Hawaii 96813, USA.
Stone
James C
JC
Blumberg
Peter M
PM
Lorenzo
Patricia S
PS
D000818:Animals; D017304:Annexin A5 / Q000737:chemistry; D017209:Apoptosis; D015153:Blotting, Western; D002454:Cell Differentiation; D002478:Cells, Cultured; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D000078404:Epidermal Cells; D004817:Epidermis / Q000378:metabolism; D005434:Flow Cytometry; D020662:Guanine Nucleotide Exchange Factors; D006160:Guanosine Triphosphate / Q000378:metabolism; D015151:Immunoblotting; D053550:Keratin-10; D015603:Keratinocytes / Q000378:metabolism; D007633:Keratins / Q000096:biosynthesis; D051379:Mice; D009374:Neoplasms, Experimental; D010703:Phorbol Esters / Q000378:metabolism*; D011233:Precipitin Tests; D011493:Protein Kinase C / Q000378:metabolism; D021381:Protein Transport; D051381:Rats; D020133:Reverse Transcriptase Polymerase Chain Reaction; D015398:Signal Transduction; D012878:Skin Neoplasms / Q000139:chemically induced; D013755:Tetradecanoylphorbol Acetate / Q000737:chemistry
D017304:Annexin A5; D004268:DNA-Binding Proteins; D020662:Guanine Nucleotide Exchange Factors; C507491:Krt10 protein, mouse; D010703:Phorbol Esters; C112278:Rasgrp1 protein, mouse; C491789:Rasgrp1 protein, rat; D053550:Keratin-10; D007633:Keratins; D006160:Guanosine Triphosphate; D011493:Protein Kinase C; D013755:Tetradecanoylphorbol Acetate