Enhanced expression of the estrogen-responsive heat shock protein HSP27 contributes to breast cancer angiogenesis and metastasis by providing mechanisms that either enhance or retard cell migration. The elucidation of these mechanisms is the long-term objective of this proposal. For example, enhanced endothelial cell migration in a wounding model, stimulated by the 18 kDa form of basic-fibroblast growth factor (FGF2), is likely to be attributable to HSP27's role as a regulator of the F-actin polymerization required for cell motility and/or HSP27 modulation of the cellular response to FGF2. To specifically address the contribution of each, a Boyden chamber system will assess the migration of HSP27-transfected endothelial and MCF-7 tumor cells to other chemotactic stimuli. MCF-7 cells do not synthesize and are not chemokinetically stimulated by FGF2, thus obviating the stimulatory influence of this hormone. These experiments will also directly test the reported correlation of breast tumor HSP27 expression with enhanced invasiveness. The F-actin structure of HSP27-transfected endothelial cells while they are migrating will be directly observed by fluorescence microscopy and video-time lapse photography. Alteration or augmentation of structures associated with migration will demonstrate that HSP27 affects migration by this mechanism. The influence of HSP27 on endothelial and tumor cell responsiveness to FGF2 will be tested by assessing FGF2 receptor expression and affinity, FGF2 uptake and processing, the FGF2 mitogenic response and the phosphorylation of proteins induced by FGF2. Enhanced Hsp27 expression can also retard endothelial cell migration. Estrogen treatment of HSP27 transfected endothelial cells induces the release of the high molecular weight (HMW) forms of FGF2 which, interestingly, inhibits the migration of these cells. Exogenous HMW FGF2 inhibits both tumor and endothelial cell migration by a mechanism that will be elucidated by performing similar experiments to those used to describe the response of cells to the 18kDa FGF2. In addition, the identification of the HMW FGF2 receptor responsible for the negative migratory signal and proteins uniquely phosphorylated by HMW FGF2 binding will be attempted. HMW FGF2 release is dependent on a direct interaction between HSP27 and HMW FGF2, the nature of which will be studied. Study of the estrogen-induced HMW release will include testing the hypothesis that the activated estrogen receptor displaces HMW FGF2 from HSP27. In addition, other consequences of the HMW FGF2/HSP27 interaction (e.g., FGF2 sequestering or nuclear translocation ) will be investigated.
| Piotrowicz, R S; Maher, P A; Levin, E G (1999) Dual activities of 22-24 kDA basic fibroblast growth factor: inhibition of migration and stimulation of proliferation. J Cell Physiol 178:144-53 |
