MHC-class-I expression in human breast cancer correlates with nuclear localization of the 90 kDa heat-shock-protein

Breast cancer cells frequently exhibit a reduction in expression of major h istocompatibility-complex (MHC) class I apoptosis. Recent studies indicate that the 90 kD heat-shock-protein (HSP90) plays a major role in the transfe r of antigenic peptides to the MHC class I complex. HSP90 is a molecular ch aperone which is involved in signal transduction and regulation of apoptosi s. Since HSP90 is described to be elevated in breast cancer, its relationsh ip with MHC class I expression was investigated Using in immunohistochemist ry we analyzed the expression and localization of HSP90 and MHC class I in 17 human breast tumors. Positive correlation (p<0.025) between strong nucle ar staining for HSP90 and high MHC class I expression was observed. In tumo rs with reduced MHC class I These findings lead to the hypothesis that tumo r cells with high MHC class I expression and susceptibility to CTL action m ay escape apoptosis by a mechanism which involves increased nuclear HSP90.