Expression and Potential Role of Fibroblast Growth Factor 2 and Its Receptors in Human Embryonic Stem Cells

Abstract

Although the detection of several components of the fibroblast growth factor (FGF) signaling pathway in human embryonic stem cells (hESCs) has been reported, the functionality of that pathway and effects on cell fate decisions are yet to be established. In this study we characterized expression of FGF-2, the prototypic member of the FGF family, and its receptors (FGFRs) in undifferentiated and differentiating hESCs; subsequently, we analyzed the effects of FGF-2 on hESCs, acting as both exogenous and endogenous factors. We have determined that undifferentiated hESCs are abundant in several molecular-mass isoforms of FGF-2 and that expression pattern of these isoforms remains unchanged under conditions that induce hESC differentiation. Significantly, FGF-2 is released by hESCs into the medium, suggesting an autocrine activity. Expression of FGFRs in undifferentiated hESCs follows a specific pattern, with FGFR1 being the most abundant species and other receptors showing lower expression in the following order: FGFR1 → FGFR3 → FGFR4 → FGFR2.Initiation of differentiation is accompanied by profound changes in FGFR expression, particularly the upregulation of FGFR1. When hESCs are exposed to exogenous FGF-2, extracellular signal-regulated kinases are phosphorylated and thereby activated. However, the presence or absence of exogenous FGF-2 does not significantly affect the proliferation of hESCs. Instead, increased concentration of exogenous FGF-2 leads to reduced outgrowth of hESC colonies with time in culture. Finally, the inhibitor of FGFRs, SU5402, was used to ascertain whether FGF-2 that is released by hESCs exerts its activities via autocrine pathways. Strikingly, the resultant inhibition of FGFR suppresses activation of downstream protein kinases and causes rapid cell differentiation, suggesting an involvement of autocrine FGF signals in the maintenance of proliferating hESCs in the undifferentiated state. In conclusion from our data, we propose that this endogenous FGF signaling pathway can be implicated in self-renewal or differentiation of hESCs.

Overexpression of BCL2 enhances survival of human embryonic stem cells during stress and obviates the requirement for serum factors

“…When bFGF was removed from the culture media, BCL2-hESCs continued to proliferate but gradually differentiated. Accumulating evidence suggests that FGF signaling plays a central role in sustaining hESCs in an undifferentiated state by providing both survival and antidifferentiation signals (8,10,11,24). Our results suggest that although BCL2 can replace the prosurvival function of bFGF, it cannot supplant the antidifferentiation signal that bFGF provides.…”

“…Although several defined media have optimized the growth and maintenance condition for hESCs without the requirement of a feeder layer, these media still rely on bFGF supplementation. FGF signaling plays a critical role in the survival, self-renewal, proliferation, and maintenance of the undifferentiated hESC state in vitro (8)(9)(10)(11)(12)(13)(14).…”

Ovarian cancer stem-like side-population cells are tumourigenic and chemoresistant

“…NANOG and OCT4 are more significantly overexpressed in poorly differentiated tumours than in well-differentiated tumours (Ben-Porath et al, 2008). These genes contribute to stem cell-like phenotypes found in many tumours (Dvorak and Hampl, 2005;Wong et al, 2008). STELLAR, also known as developmental pluripotency associated-3 (DPPA3), is expressed in human embryonic cells.…”

Calcium signaling in human pluripotent stem cells

“…Signals evoked by FGF2 seem to be indispensable for maintaining hSC pluripotent state. FGF2, in combination with three small molecule inhibitors, supports the long-term maintenance of pluripotent hESC cultures [47], while blocking the FGF receptor signaling leads to rapid differentiation of these cells [48,49]. In undifferentiated hPS cells FGF2 acts directly on FGFR by stimulating signaling pathways downstream of the receptor [50,51], as well as indirectly by modulating signals in feeder cells or in the neighboring hPSC-derived niche cells [52][53][54][55].…”