Modulation of cyclin D1 and its signaling components by the phorbol ester TPA and the tyrosine phosphatase inhibitor vanadate

Abstract

The mechanism by which 12-O-tetradecanoylphorbol-13-acetate (TPA) triggers cell-cycle progression at G1 phase in mouse embryonic fibroblast C3H 10T1/2 cells was examined. TPA treatment resulted in a temporary induction of cyclin D1 peaking at 9 h post stimulation. PD98059 (10 microM), the specific inhibitor of MAPK kinase, completely blocked TPA-stimulated cyclin D1 induction and DNA synthesis, confirming that MAPK activation plays an essential role in TPA-stimulated cell-cycle progression. Although both PKCalpha and PKCepsilon are expressed in C3H 10T1/2 cells, inhibitor studies suggest that PKCepsilon activation is required for the activation of MEK/MAPK signal transduction cascade. p70s6K, an important kinase involved in the regulation of protein synthesis and cell-cycle progression, has been reported to be activated through a PKC-dependent pathway (TPA-activatable) in addition to a PI3K-dependent pathway. Here, we demonstrate for the first time that TPA-stimulated MAPK activation is essential for the phosphorylation of several key residues involved in the activation of p70s6K, namely, thr389, thr421, and ser424. Vanadate, the tyrosine phosphatase inhibitor, triggered a sustained elevation of the level of active MAPK. However, corresponding to a rapid loss of cyclin D1 protein, vanadate treatment resulted in a significant shut out of 3H-thymidine incorporation into DNA regardless of TPA cotreatment. Vanadate treatment also led to the increase of active MEK, increased phosphorylation of p70s6K at thr389, thr421, and ser424 yet without activation of PKB. These data suggest that vanadate can selectively perturb the activation of signaling components which raises the interesting issue as to how vanadate downregulates the cyclin D1 level.

Roles of Specific Isoforms of Protein Kinase C in the Transcriptional Control of Cyclin D1 and Related Genes

“…Our results are consistent with previous evidence that the phorbol ester tumor promoter TPA, a potent activator of several isoforms of PKC, induces cyclin D1 expression in mammalian cells (24) and that TPA triggers cell cycle progression at the G 1 phase in NIH3T3 (25) and C3H 10T1/2 (24) mouse embryo fibroblast cells. In addition, Yan et al (24) reported that activation of PKC-⑀ is required for activation of the MEK/ mitogen-activated protein kinase signaling cascade during TPA-enhanced cell cycle progression in C3H 10T1/2 cells.…”

“…In addition, Yan et al (24) reported that activation of PKC-⑀ is required for activation of the MEK/ mitogen-activated protein kinase signaling cascade during TPA-enhanced cell cycle progression in C3H 10T1/2 cells. On the other hand, Besson et al (26) reported that PKC-␣ activity controls cell cycle progression in U215N human glioma cells by up-regulating the expression of p21…”

Tiam1-deficiency impairs mammary tumor formation in MMTV-c-neu but not in MMTV-c-myc mice

“…Skin tumors that were generated by treatment with DMBA only grew equally well in the presence or absence of Tiam1 (Malliri et al 2002b), indicating that TPA-induced but not DMBAinduced proliferation depends on Tiam1-mediated Rac activation. TPA is able to induce cyclin D1 expression, a regulator of cell proliferation (Yan and Wenner 2001), suggesting that Tiam1 is required for TPA-induced proliferation by inXuencing cyclin D1 levels. Moreover, both the Ras and Neu oncogenes are absolutely dependent on cyclin D1 expression for mammary tumor formation in MMTVras and MMTV-c-neu transgenic mice (Yu et al 2001).…”

Arctigenin Anti‐Tumor Activity in Bladder Cancer T24 Cell Line Through Induction of Cell‐Cycle Arrest and Apoptosis

“…Cyclin expression is characterized by its typical periodicity and phase specificity, for example, the expression of cyclin D1 initiates the cell cycle. Cyclin D1 then binds to CDK4 and CDK6 to induce cells to enter the G1 phase of the cell cycle (Yan et al, 2001). Altered expression, amplification, or mutation of these cell cycle initial genes, such as cyclin D1, CDK4, and CDK6, promote cell proliferation and tumor progression (Sherr, 1996;Malumbres et al, 2003;Santamaria et al, 2006;Molenaar et al, 2008).…”