Tumor Promotion by Depleting Cells of Protein Kinase Cδ

Lu, Zhimin; Hornia, Armand; Jiang, You Wei; Zang, Qun S.; Ohno, Shigeo; Foster, David A.

doi:10.1128/mcb.17.6.3418

Cited by 200 publications

(174 citation statements)

References 41 publications

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“…However, it must be noted that PKCd activity was associated with growth inhibition of other cells. PKCd overexpression inhibited growth of normal ®broblasts (Mischak et al, 1993), and in one study, expressing a catalytically inactive PKCd promoted transformation by c-src (Lu et al, 1997). These apparently con¯icting results indicate that e ects of increasing or decreasing PKCd activity may be context speci®c.…”

Section: Discussionmentioning

confidence: 98%

Increased protein kinase Cδ in mammary tumor cells: relationship to transformation and metastatic progression

et al. 1999

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Relatively little is known about the molecular mechanisms of tumor promotion/progression in mammary carcinogenesis. Increased protein kinase C (PKC) activity is known to promote tumor formation in several tissues; however, its role in mammary carcinogenesis is not yet known. To determine if individual PKCs may selectively regulate properties of mammary tumor cells, we compared PKC isozyme levels in mammary tumor cell lines with low, moderate and high metastatic potential. All three cell lines expressed a, d, e and z PKCs; however, PKCd levels were relatively increased in the highly metastatic cells. To determine if increased PKCd could contribute to promotion/progression, we overexpressed PKCd in the low and moderately metastatic cell lines. PKCd overexpression had no signi®cant e ect on growth of adherent cells, but signi®cantly increased anchorage-independent growth. Conversely, expressing the regulatory domain of PKCd (RDd), a putative PKCd inhibitory fragment, inhibited anchorage-independent growth. The e cacy of RDd as a PKCd inhibitor was demonstrated by showing that RDd selectively interfered with PKCd subcellular location and signi®cantly interfered with phosphorylation of the PKC cytoskeletal substrate, adducin. PKC-dependent phosphorylation of cytoskeletal substrate proteins, such as adducin, provides a mechanistic link between increased PKCd activity and phenotypic changes in cytoskeletaldependent processes such as migration and attachment, two processes that are relevant to metastatic potential. The reciprocal growth e ects of expressing PKCd and RDd as gain and loss of function constructs, respectively, provide strong evidence that PKCd regulates processes important for anchorage-independent growth in these mammary tumor cells.

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Section: Discussionmentioning

confidence: 98%

Increased protein kinase Cδ in mammary tumor cells: relationship to transformation and metastatic progression

et al. 1999

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“…Cell cultures were made quiescent by growing them to confluence and then replacing the medium with fresh medium containing 0.5% newborn calf serum for 1 day. Cells expressing the kinase-dead PKC ␣ were generated as described previously (7). The kinase-dead PKC ␣ clone was generated by a mutation to the ATP-binding site as described previously (15).…”

Section: Methodsmentioning

confidence: 99%

Activation of Protein Kinase C Triggers Its Ubiquitination and Degradation

Liu

Hornia

et al. 1998

Molecular and Cellular Biology

307

256

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Treatment of cells with tumor-promoting phorbol esters results in the activation but then depletion of phorbol ester-responsive protein kinase C (PKC) isoforms. The ubiquitin-proteasome pathway has been implicated in regulating the levels of many cellular proteins, including those involved in cell cycle control. We report here that in 3Y1 rat fibroblasts, proteasome inhibitors prevent the depletion of PKC isoforms ␣, ␦, and in response to the tumor-promoting phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA). Proteasome inhibitors also blocked the tumor-promoting effects of TPA on 3Y1 cells overexpressing c-Src, which results from the depletion of PKC ␦. Consistent with the involvement of the ubiquitin-proteasome pathway in the degradation of PKC isoforms, ubiquitinated PKC ␣, ␦, and were detected within 30 min of TPA treatment. Diacylglycerol, the physiological activator of PKC, also stimulated ubiquitination and degradation of PKC, suggesting that ubiquitination is a physiological response to PKC activation. Compounds that inhibit activation of PKC prevented both TPA-and diacylglycerol-induced PKC depletion and ubiquitination. Moreover, a kinase-dead ATP-binding mutant of PKC ␣ could not be depleted by TPA treatment. These data are consistent with a suicide model whereby activation of PKC triggers its own degradation via the ubiquitin-proteasome pathway.Tumor promotion by phorbol esters involves the selective amplification of cells previously mutated in an appropriate growth-stimulatory gene (3,17). Phorbol esters exert their effects on the protein kinase C (PKC) family of genes, which consists of genes that encode at least nine distinct isoforms that are responsive to tumor-promoting phorbol esters (9). Phorbol esters first activate phorbol ester-responsive PKC isoforms, but upon prolonged treatment, these isoforms are proteolytically degraded (16). Using a cell culture model system in which cells overexpressing c-Src were transformed by phorbol ester treatment, we recently demonstrated that the tumor-promoting effect of the phorbol ester 12-O-tetradecanoylphorbol-13-acetate (TPA) on these cells was due to the depletion of PKC ␦ (7). These data suggested that PKC ␦ may function as a tumor suppressor. Consistent with this hypothesis, PKC ␦ was inactivated by tyrosine phosphorylation in cells transformed by v-Src (19) and v-Ras (2). Thus, regulation of PKC ␦ at the level of activity and expression may be a very important cell growth control mechanism.PKC ␣ has been reported to become ubiquitinated in response to bryostatin 1, an activator of PKC that prevents tumor promotion in mouse skin by TPA (6). The ubiquitin-proteasome pathway is a nonlysosomal degradation system that controls the timed destruction of cell cycle-regulatory proteins, including the tumor suppressor p53; the cyclin-dependent kinase inhibitor p27; the cyclins; the oncogene products c-Myc, c-Jun, and c-Fos; and the transcription factors NF-B and E2F (reviewed in reference 13). This pathway involves the covalent tagging of proteins with u...

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“…Therefore, to establish further that derepression of TGF-b signaling was critical for the G 1 arrest induced by rapamycin, we examined whether suppression of PKCd, like suppression of TGF-b directly, prevented G 1 arrest by rapamycin and led to apoptosis. We first examined the effect of rottlerin, a compound that has been shown to suppress PKCd activity in vivo (Lu et al, 1997) on rapamycin-treated MDA-MB-231 cells. As shown in Figure 2d, in the presence of rottlerin, rapamycin induced apoptosis and PARP cleavage in MDA-MB-231 cells in the presence of serum.…”

Section: Tgf-b Suppresses Rapamycin-induced Apoptosis In Mda-mb-231 Cmentioning

confidence: 99%