Anti-sense inhibition of small-heat-shock-protein (HSP27) expression in MCF-7 mammary-carcinoma cells induces their spontaneous acquisition of a secretory phenotype

This work was aimed at testing the hypothesis (hitherto supported only by i ndirect evidence) that, besides contributing to resistance to stress, the s mall heat-shock-protein HSP27 might be involved in the control of growth an d differentiation in mammary-tumour cells, where it is known to be oestroge n-regulated. Therefore, MCF-7 cells were transfected with a modulatable hum an hsp27 anti-sense cDNA, Clones of transfectants (designated alpha hsp27) were selected which, upon expression of the anti-sense, exhibited a decline in HSP27 accumulation, associated with a decrease in resistance to heat sh ock and in proliferation rate, the degree of the latter reflecting their re spective reduction in HSP27 content, The effects of anti-sense inhibition o f HSP27 production were similar to those exerted on parental cells by phorb ol myristate (TPA). Both resulted in growth inhibition, accumulation of lip id droplets in the cytoplasm, formation of secretory microvesicles with int ernal microvilli and increased release of several proteins, including the i soforms of a 52-kDa protein, which we identified as the oestrogen-regulated protein cathepsin D, all this without noticeable change in actin organizat ion. These data constitute the first direct support for the hypothesis that , at least: in some cell types, HSP27 might play a modulatory role in cell differentiation and (perhaps by this) in proliferation, While allowing diss ociation of this role from the known action of HSP27 on actin polymerizatio n, they suggest similar modulation of the function of some protein(s) impli cated in the acquisition of the secretory phenotype by MCF-7 cells, with HS P27 also exerting an inhibitory action that can be alleviated either by its phosphorylation (as occurs with TPA) or by inhibition of its production. ( C) 1999 Wiley-Liss, Inc.