Hirokazu Nakahara

Involvement of Cdc42 and Rac small G proteins in invadopodia formation of RPMI7951 cells

Background:  Invadopodia are membrane protrusions into the extracellular matrix by aggressive tumour cells. These structures are associated with sites of matrix degradation and invasiveness of malignant tumour cells in an in vitro fibronectin degradation/invasion assay. The Rho family small G proteins, consisting of the Rho, Rac and Cdc42 subfamilies, are implicated in various cell functions, such as cell shape change, adhesion, and motility, through reorganization of the actin cytoskeleton. We studied the roles of the Rho family small G proteins in invadopodia formation.

RPAP3 interacts with Reptin to regulate UV‐induced phosphorylation of H2AX and DNA damage

We have previously reported that Monad, a novel WD40 repeat protein, potentiates apoptosis induced by tumor necrosis factor‐α and cycloheximide. By affinity purification and mass spectrometry, RNA polymerase II‐associated protein 3 (RPAP3) was identified as a Monad binding protein and may function with Monad as a novel modulator of apoptosis pathways. Here we report that Reptin, a highly conserved AAA + ATPase that is part of various chromatin‐remodeling complexes, is also involved in the association of RPAP3 by immunoprecipitation and confocal microscopic analysis. Overexpression of RPAP3 induced HEK293 cells to death after UV‐irradiation. Loss of RPAP3 by RNAi improved HeLa cell survival after UV‐induced DNA damage and attenuated the phosphorylation of H2AX. Depletion of Reptin reduced cell survival and facilitated the phosphorylation on H2AX. These results suggest that RPAP3 modulates UV‐induced DNA damage by regulating H2AX phosphorylation. J. Cell. Biochem. 106: 920–928, 2009.

Molecular cloning of novel Monad binding protein containing tetratricopeptide repeat domains

MINT‐6551090: Monad (uniprotkb:Q96MX6) physically interacts (MI:0218) with RPAP3 (uniprotkb:Q9H6T3) by anti tag coimmunoprecipitation (MI:0007) MINT‐6551101, MINT‐6551118: Monad (uniprotkb:Q96MX6) physically interacts (MI:0218) with RPAP3 (uniprotkb:Q9H6T3) by pull down (MI:0096) MINT‐6551132: RPAP3 (uniprotkb:Q9H6T3) physically interacts (MI:0218) with Monad (uniprotkb:Q96MX6) by anti bait coimmunoprecipitation (MI:0006)

Induction of surface CCR4 and its functionality in mouse Th2 cells is regulated differently during Th2 development.

T helper cell type 1 (Th1) and Th2 cells express distinct sets of chemokine receptors. In contrast to Th1 chemokine receptors, it is largely unknown how Th2 chemokine receptors such as CC chemokine receptor 4 (CCR4) are induced during Th2 differentiation. Here, we investigated the induction of CCR4 surface expression and ligand responsiveness evaluated by functional assays such as chemokine binding and chemotaxis. This was done in comparison with those of a Th1 chemokine receptor, CXC chemokine receptor 3 (CXCR3). Resting T cells expressed neither CXCR3 nor CCR4. CXCR3 expression and ligand responsiveness were observed when resting T cells were stimulated with anti‐CD3 plus anti‐CD28 in the presence of [interleukin (IL)‐12+anti‐IL‐4] and then recultured without T cell receptor (TCR) stimulation. Unlike CXCR3, CCR4 was induced immediately after anti‐CD3/anti‐CD28 stimulation in the presence of (IL‐4+anti‐interferon‐γ+anti‐IL‐12). However, these CCR4‐positive cells failed to exhibit chemokine binding and chemotaxis. Although the levels of surface CCR4 expression were not increased after the subsequent reculture in the absence of TCR stimulation, CCR4 responsiveness was induced in this stage of Th2 cells. The induction of CCR4 expression and the acquisition of CCR4 responsiveness did not occur in IL‐4‐deficient (IL‐4–/–) and signal transducer and activator of transcription (STAT)6–/– T cells. CCR4 expression and functionality were regained in IL‐4–/– but not in STAT6–/– T cells by the addition of recombinant IL‐4. Although surface expression and functionality of CCR4 are induced depending on the IL‐4/STAT6 signaling pathway, the present results indicate that the functionality of CCR4 does not correlate with CCR4 expression but emerges at later stages of Th2 differentiation.

Liposarcoma of the floor of the mouth: A case report

Abstract Liposarcoma is one of the most common malignant soft tissue tumors of adults. According to Enzinger and Weiss,1 the incidence ranges from 16% to 18% of all soft tissue sarcomas. The extremities, particularly the thighs, and the retroperitoneum are the most common primary sites for liposarcoma. Occurrence in the head and neck region is rare; Pack and Pierson found none in their review of 105 cases.2 The Armed Forces Institute of Pathology (AFIP) series of 1,067 liposarcomas included 60 (5.6%) in the head and neck.1 Intraoral liposarcoma is even more rare. Most of them are located in the cheek, but others have been reported in the floor of the mouth, soft palate, mandible, lip, and gingiva.3 This report presents a case of liposarcoma arising in the floor of the mouth.

Simultaneous malignant melanoma and squamous cell carcinoma of the oral cavity: A case report

Primary malignant melanoma of the oral cavity is rare. The incidence of oral melanoma constitutes between 0.2% and 8.0% of all melanomas, although higher percentages are reported in Japanese and other nonwhite races. In contrast, squamous cell carcinoma is the most common malignant neoplasm in the oral region. Multiple cancers may develop independently over the course of time in one organ, or double cancers may develop separately in different organs. Both types of cancer are collectively referred to as multiple primary cancers. The simultaneous occurrence of two histologically distinct primary malignancies in the same organ is extremely rare. We present a case of simultaneous malignant melanoma in association with squamous cell carcinoma of the oral cavity.

Inhibition of Rac Induces Hyper-Activation of c-Jun N-Terminal Kinase and Caspase-Dependent Apoptosis

Abstract Apoptosis is one mechanism by which cancer cells can be eliminated. Therefore, understanding the signaling pathways that transduce apoptotic signals in cancer cells is an indispensable component of cancer research. Rac, a member of the Rho family of proteins, has been implicated in the regulation of cell survival and apoptosis. However, the mechanisms underlying this process remain to be elucidated. To understand the role of Rac in oral squamous cancer, we inhibited its activity by a Rac-specific small molecule inhibitor, NSC23766, or transfection of dominant negative Rac (Rac-DN), and discovered that inhibition of Rac activity elicits apoptosis in highly malignant oral squamous carcinoma (OSC-19) cells. Upon suppression of Rac, we observed up-regulation of c-Jun N-terminal kinase (JNK), leading to caspase-dependent apoptosis. Furthermore, stimulation of protein phosphatase (PP5) rescued apoptosis caused by Rac inhibition by dephosphorylating JNK. Taken together, inhibition of Rac activity leads to the suppression of PP5 activity, which results in extensive activation of JNK and caspase-dependent apoptosis. In conclusion, Rac inhibition may represent a novel therapeutic approach for oral squamous carcinoma.