Effect of social housing condition on heat shock protein (HSP) expression in the Shionogi mouse mammary carcinoma (SC115)

Our previous studies have shown that social housing conditions can signific antly alter the growth rate of the Shionogi mouse mammary carcinoma (SC115) . The present study extended our investigations to the molecular level by e xamining stressor effects on the expression of a group of stress-responsive proteins, the heat shock proteins (HSPs). We hypothesized that HSP express ion in SC115 cells may be altered by (a) different social housing condition s in vivo and (b) steroid hormone and growth factor exposure in vitro. Mice were reared in groups (G) or as individuals (I). Immediately following tum or cell injection, mice were rehoused from group to individual (GI), from i ndividual to group (IG), or they remained in groups (GG). Tumor tissue was resected at 0.8 g or 3.0 g, as evidence suggests that tumor size affects HS P expression, which in turn affects proliferation. The data demonstrate tha t expression of HSP25, 70, and 90 was increased in tumors from mice in the IG compared to GG and GI mice, at both tumor weights examined. In addition, in IG mice, HSP90 expression was greater in 0.8 g compared to 3.0 g tumors . Under controlled culture conditions, hormones known to stimulate SC115 gr owth both in vivo and in vitro altered HSP expression. Physiological levels of dihydrotestosterone (DHT) and pharmacological levels of hydrocortisone (HC) upregulated expression of HSP25, whereas physiological levels of beta- estradiol (E-2) upregulated expression of HSP90. These data are the first t o demonstrate that a psychosocial stressor, a change in social housing cond ition, can induce differential HSP expression. Further, these data show tha t hormones that regulate SC115 tumor growth, also alter HSP expression.