Involved in the regulation of cell growth. May stabilize the active CDC2-cyclin B1 complex and thereby contribute to the regulation of the cell cycle and the prevention of uncontrolled cell proliferation. May act as a tumor suppressor. {ECO:0000269|PubMed:10097140, ECO:0000269|PubMed:11464283, ECO:0000269|PubMed:11504921}. This is the function of LZTS1 (leucine zipper tumor suppressor 1, ENSG00000061337).