P70 S6 Kinase alpha is a member of the RSK (ribosomal S6 kinase) family of serine/threonine kinases and contains 2 non-identical kinase catalytic domains. It phosphorylates several residues of the S6 ribosomal protein. The kinase activity of this protein is activated by serine/threonine phosphorylation and protein kinase C and inactivated by type 2A phosphatase. Activation leads to an increase in protein synthesis and cell proliferation. Overexpression of this kinase is involved in some breast cancer cell lines. Alternate translational start sites have been described and alternate transcriptional splice variants have been observed but have not been thoroughly characterized.