Cell motility is critical for the three major events in the healing of human skin wounds: re-epithelialization, angiogenesis and fibroplasia. What regulates the migration of various types of skin cells into the wound bed remains unknown. In un-wounded skin, skin cells are nourished by a plasma filtrate. When skin is wounded, skin cells at the wound edge experience an acute transition from plasma to serum. As the wound heals, there is a transition back to plasma in the newly healed environment. We found that a physiological function of this """"""""plasma >serum>plasma transition"""""""" is to orchestrate the orderly migration of human epidermal keratinocytes and human dermal fibroblasts (HDFs) (Henry et al. LANCET, 361:574-576, 2003; Bandyopadhay et al. J. Cell Biol. in press, 2006). Under these physiological conditions, we identified PDGF- BB as the major factor in human serum for HDF migration, the critical event in skin wound fibroplasias. This finding was a major advance for us because we have then been concentrating on the PDGF-BB's pro- motility signaling program for HDFs as a surrogate for human serum, which is unmanageably complex. To investigate the signaling events in primary HDFs, in which drug selection for stable cell lines is not an option, we established two lentiviral vector-derived systems that guarantee delivery of single or multiple genes (up-regulation) or siRNAs (down-regulation) into HDFs with unprecedented >90% gene transduction efficiency. With these systematic advances,we went on to identify seven signaling pathways, including FAK, Akt, Pak, PKC-delta, ERK1/2, p38 and JNK, essential for PDGF-BB-stimulated HDF migration (Li et al. Mol. Biol. Cell 15:294-305, 2004a;Fan et al. J. Invest. Derm., 2006, in press). The primary reason fordoing this way was because we found that few of these pathways alone were sufficient to promote HDF migration to the optimal level of PDGF-BB. Hence, our new challenge is how to reconstitute the """"""""multiple parallel signaling networks"""""""" that mediate PDGF-BB-induced HDF migration. To gain insights into this problem, we will focus on the tyrosine autophosphorylation sites in the PDGF receptor-beta (PDGFR-beta), which relay all PDGF-BB signals. We would like to gain insights into which of these phosphotyrosines constitutes the motility signaling network at the PDGFR level. We hypothesize that the parallel signaling networks originate at the PDGFR level.
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