Immediate-early gene. Plays an important role in embryonic development as well as in cellular growth and proliferation; its long-term silencing affects cell survival and cell cycle distribution as well as decreases CDK1 activity correlated with reduced phosphorylation of CDK1. Plays a role as a positive regulator of the sonic hedgehog pathway, acting downstream of PTCH1 (PubMed:16024801, PubMed:9372240). Plays an important role in the regulation of centriole duplication. Required for the onset of procentriole formation and proper mitotic progression. During procentriole formation, is essential for the correct loading of SASS6 and CENPJ to the base of the procentriole to initiate procentriole assembly (PubMed:22020124). Homodimer (PubMed:22020124). Interacts with PIN1 via its WW domain. This interaction is dependent on STIL mitotic phosphorylation (By similarity). Interacts with CENPJ (PubMed:22020124, PubMed:25385835). Interacts with RBM14 and this interaction interferes with the interaction of STIL with CENPJ (PubMed:25385835). Forms a complex with CENPJ and SASS6 (PubMed:22020124). Expressed in all hematopoietic tissues and cell lines. Highly expressed in a variety of tumors characterized by increased mitotic activity with highest expression in lung cancer. Down-regulated when cell proliferation ceased. Accumulates during G2 phase and falls at completion of the cell cycle. Ubiquitinated. Phosphorylated following the activation of the mitotic checkpoint. A chromosomal aberration involving STIL may be a cause of some T-cell acute lymphoblastic leukemias (T-ALL). A deletion at 1p32 between STIL and TAL1 genes leads to STIL/TAL1 fusion mRNA with STIL exon 1 splicing to TAL1 exon 3. As both STIL exon 1 and TAL1 exon 3 are 5'-untranslated exons, STIL/TAL1 fusion mRNA predicts a full-length TAL1 protein under the control of the STIL promoter, leading to inappropriate TAL1 expression. In childhood T-cell malignancies (T-ALL), a type of defect such as STIL/TAL1 fusion is associated with a good prognosis. In cultured lymphocytes from healthy adults, STIL/TAL1 fusion mRNA may be detected after 7 days of culture. The disease is caused by variants affecting the gene represented in this entry.