ABSTRACT
The Akt pathway is a well-known promoter of tumor malignancy. Akt3 is expressed as two alternatively spliced variants, one of which lacks the key regulatory serine 472 phosphorylation site. Whereas the function of full-length Akt3 isoform (Akt3/+S472) is well-characterized, that of Akt3/-S472 isoform remains unknown. Despite being expressed at a substantially lower level than Akt3/+S472 in triple-negative breast cancer cells, specific ablation of Akt3/-S472 enhanced, whereas overexpression, suppressed mammary tumor growth, consistent with a significant association with patient survival duration relative to Akt3/+S472. These effects were due to striking induction of apoptosis, which was mediated by Bim upregulation, leading to conformational activation of Bax and caspase-3 processing. Bim accumulation was caused by marked endocytosis of EGF receptors with concomitant ERK attenuation, which stabilizes BIM. These findings demonstrate an unexpected function of an endogenously expressed Akt isoform in promoting, as opposed to suppressing, apoptosis, underscoring that Akt isoforms may exert dissonant functions in malignancy.Significance: These results illuminate an unexpected function for an endogenously expressed Akt isoform in promoting apoptosis, underscoring the likelihood that different Akt isoforms exert distinct functions in human cancer. Cancer Res; 78(1); 103-14. ©2017 AACR.
Subject(s)
Apoptosis/physiology , Proto-Oncogene Proteins c-akt/metabolism , Triple Negative Breast Neoplasms/genetics , Triple Negative Breast Neoplasms/pathology , Animals , Apoptosis/genetics , Bcl-2-Like Protein 11/genetics , Bcl-2-Like Protein 11/metabolism , Caspase 3/genetics , Caspase 3/metabolism , Cell Line, Tumor , Female , Humans , Mice, Nude , Phosphorylation , Protein Isoforms/genetics , Protein Isoforms/metabolism , Proto-Oncogene Proteins c-akt/genetics , RNA Splice Sites , Serine/genetics , Serine/metabolism , Triple Negative Breast Neoplasms/mortality , Xenograft Model Antitumor Assays , bcl-2-Associated X Protein/genetics , bcl-2-Associated X Protein/metabolismABSTRACT
Macrophages are crucial to host defense, functioning in innate and cell-mediated immunity. MicroRNAs (miRNAs) are small non-coding RNA molecules that repress transcription and protein production. Little is known about miRNA expression in primary human macrophages, or about how macrophage miRNAs contribute to both normal macrophage function and to the pathogenesis of disease in humans. Using Western blot analyses, we demonstrated the production of miRNA machinery proteins by human primary macrophages. Using two different miRNA array techniques, we identified 119 miRNAs expressed by human primary macrophages, including hsa-let-7a, miR-16, -23a, 30b, -103, -146a, -212, and -378 and validated them by quantitative RT-PCR. Our findings provide a knowledge base to which macrophage miRNA expression in organ-specific macrophages or disease processes may be compared in humans.
