Deficiency of Protein Kinase Cα in Mice Results in Impairment of Epidermal Hyperplasia and Enhancement of Tumor Formation in Two-Stage Skin Carcinogenesis

Regulation of diurnal and circadian rhythms and cell proliferation are coupled in all mammals, including humans. However, the molecular mechanisms by which diurnal and circadian rhythms regulate cell proliferation are relatively poorly understood. In this study, we report that tumor growth in nude rats bearing human steroid receptor-negative MCF-7 breast tumors can be significantly accelerated by exposing the rats to light at night (LAN). Under normal conditions of an alternating light/dark cycle, proliferating cell nuclear antigen (PCNA) levels in tumors were maximal in the early light phase but remained at very low levels throughout the daily 24-hour cycle period monitored. Surprisingly, PCNA was expressed in tumors continually at a high level throughout the entire 24-hour period in LAN-exposed nude rats. Daily fluctuations of Akt and mitogen activated protein kinase activation in tumors were also disrupted by LAN. These fluctuations did not track with PCNA changes, but we found that activation of the Akt stimulatory kinase phosphoinositide-dependent protein kinase 1 (PDK1) directly correlated with PCNA levels. Expression of insulin-like growth factor 1 receptor (IGF-1R), an upstream signaling molecule for PDK1, also correlated with fluctuations of PDK1/PCNA in the LAN group. In addition, circulating IGF-1 concentrations were elevated in LAN-exposed tumor-bearing nude rats. Finally, RNAimediated knockdown of PDK1 led to a reduction in PCNA expression and cell proliferation in vitro and tumor growth in vivo, indicating that PDK1 regulates breast cancer growth in a manner correlated with PCNA expression. Taken together, our findings demonstrate that LAN exposure can accelerate tumor growth in vivo, in part through continuous activation of IGF-1R/PDK1 signaling. Cancer Res; 71(7); 2622-31. Ó2011 AACR.

Section: Discussionmentioning

confidence: 99%

Light at Night Activates IGF-1R/PDK1 Signaling and Accelerates Tumor Growth in Human Breast Cancer Xenografts

Dauchy

Tirrell

et al. 2011

“…In dermal fibroblasts, we have detected a, y, and q isozymes of PKC by Western blotting. 2 However, a and y isozymes are thought to be antitumorigenic (18)(19)(20)(21), and the role of q isozyme in dermal fibroblasts has not been well documented. Further studies on the role of various PKC isozymes in Rap1-PLCq signaling will be required for elucidation of the molecular mechanism linking tumor promotion and inflammation by TPA.…”

Section: Discussionmentioning

confidence: 99%

“…For instance, overexpression of PKChII in the colon resulted in hyperproliferation and increased sensitivity to carcinogen-induced cancer (17). In contrast, transgenic overexpression of a or y isozyme of PKC exhibited inhibitory effects on tumor promotion with TPA (18,19), and targeted disruption of the PKCa or PKCg gene resulted in increased tumor formation (20)(21)(22), indicating that these isozymes may function as tumor suppressors. Such observations led to the reassessment of the role of PKCs and suggested the involvement of non-PKC molecules in tumor promotion (15).…”

Section: Introductionmentioning

confidence: 99%

Crucial Role of Phospholipase Cε in Skin Inflammation Induced by Tumor-Promoting Phorbol Ester

Ikuta

Edamatsu

et al. 2008

In two-stage skin chemical carcinogenesis, phorbol ester 12-Otetradecanoylphorbol-13-acetate (TPA) acts as a promoter essential for clonal expansion of the initiated cells carrying the activated ras oncogenes. Although protein kinase C (PKC) isozymes are the main targets of TPA, their role in tumor promotion remains controversial. We previously reported that mice lacking a Ras/Rap effector phospholipase CE (PLCe À/À mice) exhibited marked resistance to tumor formation in the two-stage skin carcinogenesis. PLCe À/À mice also failed to exhibit basal layer cell proliferation and epidermal hyperplasia induced by TPA, suggesting a role of PLCE in tumor promotion. Here, we show that PLCe À/À mice exhibit resistance to TPA-induced skin inflammation as assessed by reduction in edema, granulocyte infiltration, and expression of a proinflammatory cytokine, interleukin-1A (IL-1A). On the other hand, the proliferative potentials of keratinocytes or dermal fibroblasts in culture remain unaffected by the PLCe background, suggesting that the PLCE's role in tumor promotion may be ascribed to augmentation of inflammatory responses. In dermal fibroblast primary culture, TPA can induce activation of the PLCE lipase activity, which leads to the induction of IL-1A expression. Experiments using small interfering RNA-mediated knockdown indicate that this activation is mediated by Rap1, which is activated by a TPA-responsive guanine nucleotide exchange factor RasGRP3. Moreover, TPA-induced activation of Rap1 and PLCE is inhibited by a PKC inhibitor GF109203X, indicating a crucial role of PKC in signaling from TPA to PLCE. These results imply that two TPA targets, RasGRP3 and PKC, are involved in TPA-induced inflammation through PLCE activation, leading to tumor promotion. [Cancer Res 2008;68(1):64-72]

“…First, in the transgenic mice expressing activator protein-1 inhibitor TAM67, tumor promotion was inhibited but hyperplasia was unaffected (45). Second, mice lacking protein kinase Ca show impaired TPA-induced epidermal hyperplasia with enhanced tumor formation (46). Third, keratin 10-null mice show increase cell proliferation but decrease tumor development in skin chemical carcinogenesis experiment (47).…”

Section: Discussionmentioning

confidence: 99%

Papilloma Development Is Delayed in Osteopontin-Null Mice: Implicating an Antiapoptosis Role for Osteopontin

Hsieh

Juliana²,

Hicks

et al. 2006

Osteopontin is a secreted, adhesive glycoprotein, whose expression is markedly elevated in several types of cancer and premalignant lesions, implicating its association with carcinogenesis. To test the hypothesis that induced osteopontin is involved in tumor promotion in vivo, osteopontin-null and wild-type (WT) mice were subjected to a two-stage skin chemical carcinogenesis protocol. Mice were initiated with 7,12-dimethylbenz(a)anthracene (DMBA) applied on to the dorsal skin followed by twice weekly application of 12-Otetradecanoylphorbol-13-acetate (TPA) for 27 weeks. Osteopontin-null mice showed a marked decrease both in tumor/ papilloma incidence and multiplicity compared with WT mice. Osteopontin is minimally expressed in normal epidermis, but on treatment with TPA its expression is highly induced. To determine the possible mechanism(s) by which osteopontin regulates tumor development, we examined cell proliferation and cell survival. Epidermis from osteopontin-null and WT mice treated with TPA thrice or with DMBA followed by TPA for 11 weeks showed a similar increase in epidermal hyperplasia, suggesting that osteopontin does not mediate TPA-induced cell proliferation. Bromodeoxyuridine staining of papillomas and adjacent epidermis showed no difference in cell proliferation between groups. However, terminal deoxynucleotidyl transferase-mediated dUTP nick end labeling analyses indicated a greater number of apoptotic cells in DMBA-treated skin and papillomas from osteopontinnull versus WT mice. These studies are the first to show that induction of the matricellular protein osteopontin facilitates DMBA/TPA-induced cutaneous carcinogenesis most likely through prevention of apoptosis.