The integrin-linked kinase regulates the cyclin D1 gene through glycogen synthase kinase 3 beta and cAMP-responsive element-binding protein-dependentpathways

The cyclin D1 gene encodes the regulatory subunit of a holoenzyme that phos phorylates and inactivates the PRE tumor suppressor protein. Cyclin D1 is o verexpressed in 20-30% of human breast tumors and is induced both by oncoge nes including those for Ras, Neu, and Src, and by the beta -catenin/lymphoi d enhancer factor (LEF)/T cell factor (TCF) pathway. The ankyrin repeat con taining serine-threonine protein kinase, integrinlinked kinase (ILK), binds to the cytoplasmic domain of beta (1) and beta (3) integrin subunits and p romotes anchorage-independent growth. We show here that ILK overexpression elevates cyclin D1 protein levels and directly induces the cyclin D1 gene i n mammary epithelial cells. ILK activation of the cyclin D1 promoter was ab olished by point mutation of a cAMP-responsive element-binding protein (CRE B)/ATF-2 binding site at nucleotide -54 in the cyclin D1 promoter, and by o verexpression of either glycogen synthase kinase-3 beta (GSK-3 beta) or dom inant negative mutants of CREB or ATF-2. Inhibition of the PI 3-kinase and AKT/protein kinase B, but not of the p38, ERK, or JNK signaling pathways, r educed ILK induction of cyclin D1 expression. ILK induced CREB transactivat ion and CREB binding to the cyclin D1 promoter CRE, Wnt-1 overexpression in mammary epithelial cells induced cyclin D1 mRNA and targeted overexpressio n of Wnt-1 in the mammary gland of transgenic mice increased both ILK activ ity and cyclin D1 levels. We conclude that the cyclin D1 gene is regulated by the Wnt-1 and ILK signaling pathways and that ILK induction of cyclin D1 involves the CREB signaling pathway in mammary epithelial cells.