PINK1 displays tissue-specific subcellular location and regulates apoptosis and cell growth in breast cancer cells.

The PINK1 gene is mutated in the germ line of patients with hereditary early-onset Parkinson disease, and PINK1 prosurvival function at neuronal mitochondria has been related with the etiology of this disease. However, the expression and function of PINK1 protein in nonneuronal tissues has not been determined yet. Here, we have analyzed PINK1 protein expression and subcellular distribution in normal and neoplastic human tissues and investigated the function of PINK1 in breast carcinoma cells. PINK1 protein, as stained by a specific anti-PINK1 monoclonal antibody, was widely expressed in human tissues, displaying high expression in epithelial tissues and in the central nervous system and lower expression in tissues of mesenchymal origin. The subcellular distribution of PINK1 was cytoplasmic granular or cytoplasmic diffuse in most tissues. In breast, PINK1 was also associated with the plasma membrane. Human neoplastic tissues ranged from high PINK1 expression in carcinomas to low expression in sarcomas. In neoplastic tissues, PINK1 displayed a diffuse cytoplasmic localization, with an additional membranous localization in breast carcinoma and squamous carcinoma of lung. In the human breast carcinoma Michigan Cancer Foundation-7 cell line, ectopic expression of cytoplasmic or mitochondrial-targeted PINK1 inhibited apoptosis triggered by hydrogen peroxide and suppressed cell growth in soft agar, whereas PINK1 silencing increased hydrogen peroxide-induced apoptosis. Together, our findings indicate that the physiologic functions of PINK1 go beyond its regulatory role of mitochondria-mediated cell survival in neurons.

Functional definition of relevant epitopes on the tumor suppressor PTEN protein.

The binding of PTEN to PDZ-domain-containing proteins appears to play an important role in the control of cell growth, motility and apoptosis. In turn, this binding can be abrogated by cleavage of the PTEN C-terminal region by caspase-3. We have generated and characterized monoclonal antibodies (mAb) directed against distinct epitopes at the C-terminal region of PTEN, and used them to define protein-binding epitopes on PTEN and to study its cleavage by caspase-3. mAb directed against epitopes at the far C-terminus of PTEN blocked binding to PTEN cognate PDZ domains and did not recognize the caspase-3 cleaved PTEN fragments. On the other hand, mAb that recognized an epitope within the C2 domain of PTEN did not prevent binding to PDZ domains, but could detect the caspase-3 cleaved PTEN fragments. The analysis of PTEN cleavage by caspase-3 revealed that the lipid phosphatase activity of PTEN controls its own degradation by interfering with the PI3-K anti-apoptotic activity. Our results define protein-binding sites on the PTEN tumor suppressor at the immunochemical level, and suggest a regulatory link between PTEN phosphatase activity, caspase-3 sensitivity and PTEN-protein interactions.