Parvin-β Inhibits Breast Cancer Tumorigenicity and Promotes CDK9-Mediated Peroxisome Proliferator-Activated Receptor Gamma 1 Phosphorylation

Abstract

The integrin-linked kinase (ILK) is a multifunctional adaptor protein and serine/threonine kinase that binds the cytoplasmic domains of ␤1-and ␤3-integrin receptor subunits (18,19,68). ILK is a key constituent of the molecular bridge between cell surface integrins and the cortical actin cytoskeleton, namely, focal adhesion complexes (32,49,57). In addition to a structural role, integrin-extracellular matrix (ECM) engagement or stimulation with growth factors activates ILK kinase activity in a phosphatidylinositol 3Ј kinase-dependent manner, resulting in phosphorylation of downstream substrates, such as AKT Ser473 and glycogen synthase kinase 3␤ Ser9 (13). ILK also provides integrins with a connection to certain receptor tyrosine kinases via the adaptor proteins PINCH1/2 and NCK2 (64, 72). Overexpression of ILK in cell lines results in anchorage-independent growth, E-cadherin loss, increased invasiveness, and tumorigenicity in nude mice (13,19). Moreover, increased ILK expression and activity in mouse mammary tumor virus ILK transgenic mice leads to mammary hyperplasias and breast cancers (67). These data suggest that ILK activity must be regulated carefully for effective tumor suppression in vivo and raise the possibility that modulators of ILK function or kinase activity could be deregulated during epithelial oncogenesis.Parvin-␣, -␤, and -␥ comprise a small family of widely expressed ILK-binding proteins with tandem calponin homology domains (30,48,51,57,70). The two best-characterized members, Parvin-␣ and -␤, interact directly with the ILK kinase domain in a mutually exclusive manner (73) and modulate both its kinase activity and connections to the actin cytoskeleton (51), although the molecular mechanisms underlying these actions are only now beginning to emerge (43,66,73). Less is known about Parvin-␥ function.Data from several studies suggest that Parvin-␣ and Parvin-␤ may have divergent actions in the regulation of ILK signaling and cytoskeletal dynamics. For example, Parvin-␣ was reported to facilitate ILK-mediated phosphorylation of AKT Ser473, with subsequent protection from apoptosis (13, 73), whereas Parvin-␤ overexpression in HeLa cells promoted apoptosis (73). Parvin-␤ also inhibited ILK kinase activity and reduced AKT Ser473 and glucogen synthase kinase 3␤ Ser9 phosphorylation in response to epidermal growth factor stimulation, as previously reported by us (43), consistent with negative regulation of ILK signaling. In contrast to Parvin-␣, Parvin-␤ directly bound to the actin-binding protein ␣-actinin and was required for proper focal adhesion formation, lamellipodium maturation, and cell spreading (69, 70). In addition to its reg-* Corresponding author. Mailing address:

CDK9 Regulates AR Promoter Selectivity and Cell Growth through Serine 81 Phosphorylation

“…CDK9 regulates the differentiation of 3T3-L1 cells through a direct interaction with and phosphorylation of PPAR␥, which increases PPAR␥ transcriptional activity (44). In MDA-MB-231 cells, PPAR␥ phosphorylation by CDK9 increases lipogenic gene expression (45). Thus, our work here parallels observations on PPAR␥.…”

“…Rather, we show that the RNAPPII CTD S2 kinase, CDK9, phosphorylates the AR on S81 and that this phosphorylation is required for optimal AR-mediated cell growth, likely due to the S81 phosphorylation regulating AR transcriptional activity on a selective subset of AR target genes. In addition to the AR, data suggest that the peroxisome proliferator-activated receptor ␥ (PPAR␥) is phosphorylated by CDK9 (44,45). CDK9 regulates the differentiation of 3T3-L1 cells through a direct interaction with and phosphorylation of PPAR␥, which increases PPAR␥ transcriptional activity (44).…”

Integrin signalling adaptors: not only figurants in the cancer story

“…Recently, a new function of ILK in the regulation of the microtubule cytoskeleton and mitotic spindle organization has been proposed 103 High levels of PARVIN correlate with increased cell adhesion, induce reversal of anchorageindependent growth 36 , and attenuation of tumour growth in nude mice 110 . The latter tumoursuppressive role of PARVIN is consistent with deletions observed in its locus (22q13.21) in some colon and breast cancer cells 111 .…”

Actopaxin (α-Parvin) Phosphorylation Is Required for Matrix Degradation and Cancer Cell Invasion

“…In breast cancer cell lines and advanced breast tumors mRNA and proteins levels of ␤-parvin are decreased (54), thus allowing for increased actopaxin-ILK binding and potentially increased actopaxin phosphorylation and signaling. Interestingly, the MDA-MB-231 breast cancer cells have been reported to lack ␤-parvin expression entirely (55), and we show that these cells have elevated actopaxin phosphorylation compared with normal breast epithelial cells. Forced expression of ␤-parvin in these cells inhibits proliferation and tumor growth (55), and overexpression of nonphosphorylatable Quint actopaxin inhibits cell invasion; thus, actopaxin phosphorylation may contribute to both tumor growth and metastasis.…”

“…Interestingly, the MDA-MB-231 breast cancer cells have been reported to lack ␤-parvin expression entirely (55), and we show that these cells have elevated actopaxin phosphorylation compared with normal breast epithelial cells. Forced expression of ␤-parvin in these cells inhibits proliferation and tumor growth (55), and overexpression of nonphosphorylatable Quint actopaxin inhibits cell invasion; thus, actopaxin phosphorylation may contribute to both tumor growth and metastasis. The analysis of actopaxin levels and phosphorylation in human cancer cells and tumors is incomplete, and further studies will determine the in vivo significance of actopaxin phosphorylation through the use of mouse tumor and metastasis models.…”