Exploring the global gene expression programs and regulation in the response of quiescent human fibroblasts to distinct proliferative stimuli
Serum treatment of quiescent human dermal fibroblasts induces proliferation coupled with a complex physiological response that is indicative of their normal role in wound-healing. However, it is not known to what extent such complex transcriptional events are specific to a given cell type and signal, and to what extent these changes are innate programmed responses that are activated in a range of related cell types in response to a variety of stimuli. We have profiled the global transcriptional program of human fibroblasts from two distinct tissue sources to four different growth stimuli and identified a striking conservation in their gene expression signatures. However, there were specific differences among different stimuli with regard to signaling pathways that mediate these transcriptional programs. The use of a specific PI3-kinase pathway inhibitor suggested that this pathway is differentially involved in mediating the responses of cells to serum as compared to individual peptide growth factors. By applying siRNA knockdown technique, we demonstrated that putative targets of two important immediate early transcription factors, Myc and SRF, served functions related to cell cycle progression/cell survival and wound healing, indicating that these two transcription factors may serve as master transcription controllers during the transition of fibroblasts from quiescence to proliferation. In addition, different Myc targets were identified either between different cell types (Hela vs. foreskin fibroblasts) or between different cell states (unsynchronized vs. synchronized), while SRF targets included a group of genes only induced at certain time points during cell cycle progression, which was not observed in the Myc data. MicroRNA (miRNA) expression profiling indicated that let7 and other miRNAs with similar expression profiles may be involved in regulating the transcriptional program in response to proliferative signals. Our results indicate that conservation of transcriptional programs and their regulation among different cell types may be much broader than previously appreciated.