Five of six protein kinase C isoenzymes present in normal mucosa show reduced protein levels during tumor development in the human colon

Kahl‐Rainer, Patrizia; Karner‐Hanusch, Judith; Weiß, W.; Marian, Brigitte

doi:10.1093/carcin/15.4.779

Cited by 69 publications

(40 citation statements)

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“…Alterations in several PKC isoforms occur during colonic malignant transformation, including loss of PKC-d in neoplastic progression (Weinstein, 1991;DeRubertis, 1992, 1994;Davidson et al, 1994;Kahl-Rainer et al, 1994McGarrity and Peiffer, 1994;Wali et al, 1995). Caco-2 cells, derived from a human colon cancer, also show downregulation of PKC-d (Cerda et al, 2001;Banan et al, 2002).…”

Section: Discussionmentioning

confidence: 99%

“…While PKC signaling regulates postmitotic events during normal intestinal epithelial cell maturation (Saxon et al, 1994), derangements in PKC isoforms are also thought to contribute to colonic malignant transformation. For example, PKC a, bI, d and z are decreased at different stages of neoplastic progression (Weinstein, 1991;McGarrity and Peiffer, 1994;Kahl-Rainer et al, 1994Brasitus and Bissonnette, 1998;Verstovsek et al, 1998;Black, 2001). These changes in specific isoforms suggest that PKC signal dysregulations contribute to neoplastic transformation.…”

Section: Introductionmentioning

confidence: 99%

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Protein kinase C delta inhibits Caco-2 cell proliferation by selective changes in cell cycle and cell death regulators

et al. 2006

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PKC-d is a serine/threonine kinase that mediates diverse signal transduction pathways. We previously demonstrated that overexpression of PKC-d slowed the G1 progression of Caco-2 colon cancer cells, accelerated apoptosis, and induced cellular differentiation. In this study, we further characterized the PKC-d dependent signaling pathways involved in these tumor suppressor actions in Caco-2 cells overexpressing PKC-d using a Zn 2 þ inducible expression vector. Consistent with a G1 arrest, increased expression of PKC-d caused rapid and significant downregulation of cyclin D1 and cyclin E proteins (50% decreases, Po0.05), while mRNA levels remained unchanged. The PKC agonist, phorbol 12-myristate 13-acetate (TPA, 100 nM, 4 h), induced two-fold higher protein and mRNA levels of p21 Waf1, a cyclin-dependent kinase (cdk) inhibitor in PKC-d transfectants compared with empty vector (EV) transfected cells, whereas the PKC-d specific inhibitor rottlerin (3 lM) or knockdown of this isoenzyme with specific siRNA oligonucleotides blocked p21Waf1 expression. Concomitantly, compared to EV control cells, PKC-d upregulation decreased cyclin D1 and cyclin E proteins co-immunoprecipitating with cdk6 and cdk2, respectively. In addition, overexpression of PKC-d increased binding of cdk inhibitor p27Kip1 to cdk4. These alterations in cyclin-cdks and their inhibitors are predicted to decrease G1 cyclin kinase activity. As an independent confirmation of the direct role PKC-d plays in cell growth and cell cycle regulation, we knocked down PKC-d using specific siRNA oligonucleotides. PKC-d specific siRNA oligonucleotides, but not irrelevant control oligonucleotides, inhibited PKCd protein by more than 80% in Caco-2 cells. Moreover, PKC-d knockdown enhanced cell proliferation (B1.4-2-fold, Po0.05) and concomitantly increased cyclin D1 and cyclin E expression (B1.7-fold, Po0.05). This was a specific effect, as nontargeted PKC-f was not changed by PKC-d siRNA oligonucleotides. Consistent with accelerated apoptosis in PKC-d transfectants, compared to EV cells, PKC-d upregulation increased proapoptotic regulator Bax two-fold at mRNA and protein levels, while antiapoptotic Bcl-2 protein was decreased by 50% at a post-transcriptional level. PKC-d specific siRNA oligonucleotides inhibited Bax protein expression by more than 50%, indicating that PKC-d regulates apoptosis through Bax. Taken together, these results elucidate two critical mechanisms regulated by PKC-d that inhibit cell cycle progression and enhance apoptosis in colon cancer cells. We postulate these antiproliferative pathways mediate an important tumor suppressor function for PKC-d in colonic carcinogenesis.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Protein kinase C delta inhibits Caco-2 cell proliferation by selective changes in cell cycle and cell death regulators

et al. 2006

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“…Furthermore, decreased levels of PKC activity have also been observed in preneoplastic colonic mucosa and in colonic adenomas (26 -28), suggesting that alterations in PKC expression and activities may occur early in the multistage process of colon carcinogenesis. Of the 10 or so PKC isoforms, decreased levels of PKC isoforms ␣, ␤I, ⑀, , ␦, and in human and rodent colonic tumors have been reported, with the loss of ␣, ␤I, and reported to be an early event during intestinal carcinogenesis (25,26,29,30). As well as PKC, it cannot be excluded that MutY may be phosphorylated by other kinases.…”

Section: Discussionmentioning

confidence: 99%

Defective Human MutY Phosphorylation Exists in Colorectal Cancer Cell Lines with Wild-type MutY Alleles

Parker¹,

O’Meally²,

Şahin³

et al. 2003

Journal of Biological Chemistry

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Oxidative DNA damage can generate a variety of cytotoxic DNA lesions such as 8-oxoguanine (8-oxoG), which is one of the most mutagenic bases formed from oxidation of genomic DNA because 8-oxoG can readily mispair with either cytosine or adenine. If unrepaired, further replication of A⅐8-oxoG mispairs results in C:G to A:T transversions, a form of genomic instability. We reported previously that repair of A⅐8-oxoG mispairs was defective and that 8-oxoG levels were elevated in several microsatellite stable human colorectal cancer cell lines lacking MutY mutations (human MutY homolog gene, hmyh, MYH MutY homolog protein). In this report, we provide biochemical evidence that the defective repair of A⅐8-oxoG may be due, at least in part, to defective phosphorylation of the MutY protein in these cell lines. In MutY-defective cell extracts, but not extracts with functional MutY, A⅐8-oxoG repair was increased by incubation with protein kinases A and C (PKA and PKC) and caesin kinase II. Treatment of these defective cells, but not cells with functional MutY, with phorbol-12-myristate-13-acetate also increased the cellular A⅐8-oxoG repair activity and decreased the elevated 8-oxoG levels. We show that MutY is serine-phosphorylated in vitro by the action of PKC and in the MutY-defective cells by phorbol-12-myristate-13-acetate but that MutY is already phosphorylated at baseline in proficient cell lines. Finally, using antibody-isolated MutY protein, we show that MutY can be directly phosphorylated by PKC that directly increases the level of MutY catalyzed A⅐8-oxoG repair.

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“…Experimental models of colon carcinogenesis have provided evidence of changes in PK-C both in premalignant and malignant epithelial cells; these changes include translocation of PK-C and subsequent down-regulation of this enzyme (31). Alterations in the content of specific PK-C isozymes have been also described in colon tumors with respect to normal tissue either in human samples or in experimental animal models (32,33); however, different laboratories have reported contrary results of these analyses (32,34,35). Therefore, at the present, it is not clear whether the initial activation or the later down-regulation are related to colon tumorigenesis, neither the role of specific isoforms in this process.…”

Section: Cpkc-␣ Regulates Cell Growth and Invasionmentioning

confidence: 96%

Protein Kinase C-α Activity Inversely Modulates Invasion and Growth of Intestinal Cells

Batlle¹,

Verdú²,

Domı́nguez³

et al. 1998

Journal of Biological Chemistry

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The phorbol ester phorbol 12-myristate 13-acetate induces remarkable phenotypic changes in intestinal HT-29 M6 cells; these changes consist of loss of homotypic adhesion and inactivation of E-cadherin. In parallel, cell growth is retarded. We have transfected HT-29 M6 cells with an activated form of the conventional protein kinase C␣ (cPK-C␣). Expression of this isoform induced the acquisition of a scattered phenotype, similar to that adopted by cells after addition of phorbol 12-myristate 13-acetate, with very low cell-to-cell aggregation and undetectable levels of functional E-cadherin. These cell clones were highly motile and rapidly invaded embryonic chick heart fragments. Furthermore, cells expressing activated-cPK-C␣ showed decreased proliferation in comparison to control clones. We have also studied how these two apparently antagonistic changes affect the tumorigenic ability of HT-29 M6 cells. When the different cell clones were xenografted into athymic mice, the effect on cell growth seemed to predominate. Expression of activated-cPK-C␣ significantly reduced the size of the tumors; the cells with the highest level of expression did not even form subcutaneous tumors. Besides their smaller size, the morphology of these tumors was clearly different from those originated by HT-29 M6 cells, and they could be defined as infiltrative on anatomo-pathological basis. These results indicate that cPK-C␣ controls both cell-to-cell adhesion and proliferation of intestinal cells.

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Five of six protein kinase C isoenzymes present in normal mucosa show reduced protein levels during tumor development in the human colon

Cited by 69 publications

References 0 publications

Protein kinase C delta inhibits Caco-2 cell proliferation by selective changes in cell cycle and cell death regulators

Protein kinase C delta inhibits Caco-2 cell proliferation by selective changes in cell cycle and cell death regulators

Defective Human MutY Phosphorylation Exists in Colorectal Cancer Cell Lines with Wild-type MutY Alleles

Protein Kinase C-α Activity Inversely Modulates Invasion and Growth of Intestinal Cells

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