Basic Fibroblast Growth Factor and N-Cadherin Maintain Rat Granulosa Cell and Ovarian Surface Epithelial Cell Viability by Stimulating the Tyrosine Phosphorylation of the Fibroblast Growth Factor Receptors

Abstract

Both granulosa cells (GCs) and ovarian surface epithelial cells undergo apoptosis in vivo. Although basic fibroblast growth factor (bFGF) and N-cadherin-mediated cell contact inhibit GC apoptosis, little is known about the factors that influence rat ovarian surface epithelial (ROSE) cell apoptosis. The present studies were designed to determine whether bFGF and N-cadherin maintain the viability of both GC and ROSE cells by stimulating separate signaling pathways. For the GC studies, large GCs were collected from immature rat ovaries after Percoll gradient centrifugation and placed in serum-free culture for 24 h. These studies confirmed that about 10% of the aggregated GCs and more than 50% of single GCs were apoptotic after culture. bFGF reduced the percentage of apoptotic single GCs, but did not influence aggregated GCs. A neutralizing antibody to bFGF blocked bFGF's antiapoptotic action, but did not alter the percentage of apoptotic aggregated GCs. The antibody to N-cadherin not only increased the percentage of aggregated apoptotic GCs, but also blocked bFGF's ability to maintain the viability of single GCs. The effect of the FGF receptor antibody was similar to that of the N-cadherin antibody. Like GCs, ROSE cells also undergo apoptosis in serum-free medium. Exposure to either the N-cadherin or FGF receptor antibody, even in the presence of serum, increased the percentage of apoptotic aggregated ROSE cells. As tyrosine kinase activity is involved in maintaining cell viability, the pattern of tyrosine-phosphorylated proteins was examined after culture in control (ascites) or N-cadherin antibody-supplemented medium. Exposure to the N-cadherin antibody altered the pattern of tyrosine-phosphorylated proteins, decreasing the tyrosine phosphorylation of proteins in the 130- to 180-kDa range and increasing the tyrosine phosphorylation of one or more proteins of about 50 kDa. The identity of the 50-kDa protein is unknown. However, immunoprecipitation studies demonstrated that the N-cadherin antibody reduced the amount of tyrosine-phosphorylated FGF receptor in both GCs and ROSE cells by 50%. This decrease corresponds to an increase in apoptosis among aggregated cells. Taken together, these data suggest that homophilic N-cadherin binding and bFGF-FGF receptor binding activate signal transduction pathways that converge at the level of the FGF receptor and subsequently promote the viability of both GC and ROSE cells.

T‐cadherin and signal‐transducing molecules co‐localize in caveolin‐rich membrane domains of vascular smooth muscle cells

“…Cadherins are known to participate in cell‐cell adhesion, establishment of cell polarity and morphogenesis in a variety of organs [36–41]. Emerging data suggest that their function is not limited to physical adhesion between cells, but may involve generation of intracellular signals [42, 43]. While some data supporting an important role of signalling in cadherin function have been obtained [44, 45], the mechanisms of signal transduction by cadherins are still obscure.…”

Soluble N‐cadherin stimulates fibroblast growth factor receptor dependent neurite outgrowth and N‐cadherin and the fibroblast growth factor receptor co‐cluster in cells

“…The response to the soluble NCAD‐Fc was shown to be dependent on neuronal FGF receptor function, and this suggests that it involves activation of the same signal transduction cascade that we and other researchers have established to be important for the response stimulated by cell expressed or substrate bound N‐cadherin. Interestingly, an N‐cadherin/FGF receptor pathway has been implicated in the contact dependent survival of granulosa cells (Trolice et al . 1996), and in the pathway whereby N‐cadherin stimulates migration of human breast cancer cells (Nieman et al .…”

“…When productive contacts mediated by N‐cadherin are disrupted in granulosa cells by antibody perturbation, there is a correlated decrease in the activation state of the FGF receptor and the cells eventually die as a consequence of loss of a contact dependent survival signal (Trolice et al . 1997).…”

“…1997; Lom et al . 1998) in granulosa cells (Trolice et al . 1997) and in human breast cancer cells lines (Nieman et al .…”

Gonadotropins mediate DNA synthesis and protection from spontaneous cell death in human ovarian surface epithelium

“…In sheep, apoptosis of OSE cells contiguous with the apical wall of the dominant follicle occurs with the approach of ovulation (16) . OSE cell survival in vitro can be mediated by a variety of factors including N cadherin/fibroblast growth factor (FGF) receptors (17) , mullerian inhibiting substance (18) , EGF (19) , the synthetic androgen mibolerone (20) transforming growth factor (TGF)b, and activin (21) . Finally, hCG-mediated survival of human OSE cells has been reported to correlate with upregulation of insulin-like growth factor (IGF)-1 (10) .…”