Kazushi Inoue, MD PhD
Assistant Professor of Pathology (Tumor Biology)
Cancer Biology; Molecular Medicine Graduate Program
Faculty Profile
Tel: 336-716-5863
Lab: 336-716-6047
Fax: 336-716-6757
kinoue@wakehealth.edu
Current Research:
Research in our laboratory has been focused on the understanding the regulatory mechanisms of the Dmp1-Arf-p53 pathway and how it is disrupted in human cancer. INK4a/ARF located on human chromosome 9p21 is inactivated in nearly 40% of human cancers, at a frequency estimated to be close to that of the P53 locus. This locus encodes two distinct tumor suppressor proteins: p16INK4a, which specifically binds to CDK4 to inhibit Rb phosphorylation by CDKs; and p14ARF (p19Arf in mice), which binds and negatively regulates HDM2, thereby stabilizing and activating P53. p19Arf is induced by potentially oncogenic signals stemming from overexpression of oncogenes such as c-Myc, E1A, E2F-1, and activated Ras. This quenches inappropriate mitogenic signaling by diverting early stage cancer cells to undergo p53-dependent and p53-independent growth arrest or cell death (Figure).
A series of nuclear proteins other than E2F and Myc regulate Arf expression (Figure). Dmp1 (cyclin D binding myb-like protein 1; also called Dmtf1: cyclin D binding myb-like transcription factor 1) is a novel transcription factor that was isolated in yeast two-hybrid screen of T-lymphocyte library with cyclin D2 bait. Dmp1 directly binds and activates the Arf promoter, induces cell cycle arrest in Arf-dependent fashion. p19Arf function is significantly attenuated in Dmp1-null cells, and the knockout mice show hypersensitivity to tumor formation in response to carcinogen or ?-irradiation. When crossed onto a Dmp1+/- or Dmp1-/- background, lymphomas induced by the Eµ-Myc transgene were greatly accelerated, and surprisingly, with no differences between cohorts lacking one or two Dmp1 alleles. The frequency of Arf deletion or p53 mutation was significantly lower in Dmp1+/- and Dmp1-/- tumors. Thus, Dmp1 is haplo-insufficient for tumor suppression and is a physiological regulator of the Arf-p53 pathway in vivo.
We have been searching for positive and negative regulators for the Dmp1 promoter as well as for the Arf promoter. We recently found that the Dmp1 promoter was efficiently activated by oncogenic RasV12 as well as by constitutively active c-Raf, MEK1/2, and ERK1/2 in primary cells (Figure). p19Arf did not significantly accumulate in response to oncogenic Raf signaling in Dmp1-null cells and the cells were very refractory to Raf-mediated cell cycle arrest, suggesting the critical role of Dmp1 to convey Ras-Raf-MEK-ERK oncogenic signaling to the Arf-p53 tumor suppressor pathway. Accordingly, the survival of K-rasLA mice was significantly shortened in both Dmp1+/- and Dmp1-/-mice. The Dmp1 gene was hemizygously deleted in ~40% of lung carcinomas from wild-type K-rasLA mice, demonstrating the primary involvement of Dmp1 in K-rasLA lung tumors. The Dmp1 promoter is repressed by overexpression of E2Fs and physiological mitogens. We recently found that the Dmp1-Arf pathway is inhibited by NF-?B in response to genotoxic stimuli (Figure).
The role of human DMP1 (hDMP1) in human cancer remained poorly understood. We recently analyzed ~50 pairs of human non-small cell lung cancer samples and found that loss of heterozygosity (LOH) of hDMP1 was found in ~35% of the cases, especially those which retained wild-type INK4a/ARF and/or P53. We also confirmed significant downregulation of the DMP1 protein in human lung cancers that showed LOH for hDMP1. Our data indicate the critical role of hDMP1 in suppressing human lung cancers.
Other projects in our lab include 1) mechanism and significance of post-translational modification of Dmp1, 2) identification of Dmp1-interacting proteins, 3) roles of Dmp1 in mammary gland development and breast cancer, 4) isolation of novel tumor suppressor genes from human breast cancer (multi-investigator project in the Comprehensive Cancer Center).
Figure Legend: Critical role of Dmp1 in Ras-Arf-p53 signaling. Arf is induced by potentially oncogenic signals stemming from overexpression of oncogenes such as c-Myc, E2F-1, and activated Ras. This quenches inappropriate mitogenic signaling by diverting incipient cancer cells to undergo p53-dependent and independent growth arrest or cell death. Arf expression is repressed by a number of nuclear proteins, such as Bmi1, Twist, Tbx, and Pokemon. Dmp1 directly binds and activates the Arf promoter, induces cell cycle arrest in Arf-dependent fashion. Both Dmp1-null and heterozygous mice show hypersensitivity to develop tumors in response to carcinogen DMBA and ?-irradiation. This phenotype could be explained by the inactivation of Arf-Mdm2-p53 pathway in the absence of the functional Dmp1 protein, although it is possible that Dmp1 has other targets than Arf. D-type cyclins inhibit Dmp1’s transcriptional activity in Cdk-independent fashion when E2Fs do not bind to the same promoter; however, D-cyclins cooperate with Dmp1 to activate the Arf promoter. The Dmp1 promoter is efficiently activated by the oncogenic Ras-Raf-MEK-ERK-Jun pathway. The induction of Arf by oncogenic Ras is largely dependent on Dmp1. The Dmp1 transcription is repressed by physiological mitogenic signaling as well as by overexpression of E2F proteins. We recently reported that the Dmp1-Arf pathway was inhibited by NF-?B proteins in response to genotoxic stress signaling.
Publications
See Dr. Inoue's Faculty Profile