Distinctive role of SIK1 and SIK3 isoforms in aerobic glycolysis and cell growth of breast cancer through the regulation of p53 and mTOR signaling pathways.

The Salt-inducible kinase (SIKs) belongs to an AMPK-related family kinase, an isoform of the SIK family, SIK1 gets frequently downregulated in various types of cancer contribute to tumorigenesis. However, its precise role in breast cancer and the relevant molecular mechanism remains unclear. Herein, analysis of the clinical data reveals that SIK1 expression was significantly downregulated in breast cancer tissues, and closely associated with poor survival rate in breast cancer. SIK1 is functionally stimulating oxidative phosphorylation, which in turn inhibits aerobic glycolysis and cell proliferation in breast cancer cells. Mechanistically, SIK1 directly interacted with p53 and positively regulates its transcriptional activity, thereby facilitates oxidative phosphorylation in breast cancer cells. The knockdown of SIK1 downregulates p53 transcriptional activity, leading to stimulation of aerobic glycolysis and cell proliferation. Moreover, high expression of SIK3 stimulates mTOR-mediated aerobic glycolysis and cell proliferation of breast cancer cells. These findings suggest that SIK isoforms plays distinct role in aerobic glycolysis and cell growth of breast cancer, attenuated SIK1/p53 signaling suppresses oxidative phosphorylation and growth inhibitory effect in breast cancer cells, while enhanced SIK3/mTOR signaling potentiates aerobic glycolysis mediated cell growth in breast cancer cells.