Figure 5.

TβR-I protein expression in total lysate, cytosol, and membrane fractions from human breast cell lines. Aliquots (10 μg) of total cell lysate and fractionated protein were analyzed by SDS-PAGE electrophoresis, transferred to PVDF membranes, blocked with 5% nonfat dry milk in PBS-T, and incubated with TβR-I antibody. Bound antibodies were detected by incubation with peroxidase-conjugated antirabbit immunoglobulin and enhanced chemiluminscent autoradiography. A 55-kDa band corresponding to the presence of TβR-I protein in total lysate, cytosolic, and membrane-bound protein fractions was observed. Membrane-bound fractions (and to a lesser extent the total cellular lysate) contain two (or three in the case of MCF-7) bands of close molecular weight, the significance of which remains to be determined.