Reciprocal knock-in mice to investigate the functional redundancy of lamin B1 and lamin B2.

Lamins B1 and B2 (B-type lamins) have very similar sequences and are expressed ubiquitously. In addition, both Lmnb1- and Lmnb2-deficient mice die soon after birth with neuronal layering abnormalities in the cerebral cortex, a consequence of defective neuronal migration. The similarities in amino acid sequences, expression patterns, and knockout phenotypes raise the question of whether the two proteins have redundant functions. To investigate this topic, we generated "reciprocal knock-in mice"-mice that make lamin B2 from the Lmnb1 locus (Lmnb1(B2/B2)) and mice that make lamin B1 from the Lmnb2 locus (Lmnb2(B1/B1)). Lmnb1(B2/B2) mice produced increased amounts of lamin B2 but no lamin B1; they died soon after birth with neuronal layering abnormalities in the cerebral cortex. However, the defects in Lmnb1(B2/B2) mice were less severe than those in Lmnb1-knockout mice, indicating that increased amounts of lamin B2 partially ameliorate the abnormalities associated with lamin B1 deficiency. Similarly, increased amounts of lamin B1 in Lmnb2(B1/B1) mice did not prevent the neurodevelopmental defects elicited by lamin B2 deficiency. We conclude that lamins B1 and B2 have unique roles in the developing brain and that increased production of one B-type lamin does not fully complement loss of the other

ヒットするゲーム制作のプロセス研究 ― M-GTAを用いたゲームクリエイターの質的調査 ―

departmental bulletin pape

Biological Characteristics of Two New Cell Straines Isolated from a Primary Squamous Cell Carcinoma of the Tongue and a Nodal Metastasis

本論文の要旨の一部は,第46回日本口腔外科学会総会(2001年10月,鹿児島市),第27回頭頚部腫瘍学会(2002年6月,千葉市),第39回日本口腔組織培養学会(2002年11月,福岡市)において発表した

Characterization of Tumor-Derived B56gamma Mutations and Their Effect on Tumor Suppressor Function of B56gamma PP2A

The heterotrimeric PP2A holoenzyme consists of a scaffolding A, a catalytic C, and a variable regulatory B subunit. Previous study has reported that B56gamma subunit mediates the tumor suppressive function of PP2A. B56gamma specific PP2A inhibits cell transformation by dephosphorylating and activating p53. In addition, B56gamma specific PP2A possesses the p53 independent tumor suppressive function although its mechanism is unclear. In the present study, we demonstrate the mechanism of B56gamma tumor suppressive function inactivation through characterizing B56gamma mutations identified in human cancer. First, we demonstrate that the A383G and F395C mutations disrupt B56gamma from interacting and activating p53. The mutants are unable to dephosphorylate p53 and thus lack the p53 dependent tumor suppressive function. Moreover, we identify the region adjacent to these mutations as the p53 binding domain. This finding implies that the bridging interaction between B56gamma and p53 is required for p53 dephosphorylation by PP2A. Second, we show that the C39R mutation within the HEAT repeat 1 disrupts B56gamma binding with the AC core and thus abolishes the B56gamma tumor suppressive function completely. We further demonstrate that the intact HEAT repeat 1 is required for B56gamma to bind the AC core, providing structural insights into the B56gamma specific PP2A holoenzyme assembly. Further characterization of additional B56gamma mutations reveals two classes of mutations with different mechanisms of tumor suppressive function inactivation. Mutations in the first class disrupt the interaction between B56gamma and the AC core and thus fail to regulate all substrates and completely lose the tumor suppressive function. Mutations in the second class prevent specific substrates from binding B56gamma and partially reduce the tumor suppressive function. Although it remains to be investigated how frequently these mutations occur, our results underline the importance of B56gamma tumor suppressive function in human cancer.Finally, we identified the S220N mutation that specifically disrupts the p53 independent tumor suppressive function of B56gamma, suggesting that it may disrupt the binding of unknown substrates. Identification of these proteins would contribute to the further understanding of the tumor suppressor role of B56gamma in cells

B56γ Tumor-Associated Mutations Provide New Mechanisms for B56γ-PP2A Tumor Suppressor Activity

UNLABELLED: The hetero-trimeric PP2A serine/threonine phosphatases containing the regulatory subunit B56, and in particular B56γ, can function as tumor suppressors. In response to DNA damage, the B56γ subunit complexes with the PP2A AC core (B56γ-PP2A) and binds p53. This event promotes PP2A-mediated dephosphorylation of p53 at Thr55, which induces expression of p21, and the subsequent inhibition of cell proliferation and transformation. In addition to dephosphorylation of p53, B56γ-PP2A also inhibits cell proliferation and transformation by a second, as yet unknown, p53-independent mechanism. Here, we interrogated a panel of B56γ mutations found in human cancer samples and cell lines and showed that these mutations lost B56γ tumor-suppressive activity by two distinct mechanisms: one is by disrupting interactions with the PP2A AC core and the other with B56γ-PP2A substrates (p53 and unknown proteins). For the first mechanism, due to the absence of the C catalytic subunit in the complex, the mutants are unable to mediate dephosphorylation of any substrate and thus failed to promote both the p53-dependent and -independent tumor-suppressive functions of B56γ-PP2A. For the second mechanism, the mutants lacked specific substrate interactions and thus partially lost tumor-suppressive function, i.e., either the p53-dependent or p53-independent contingent upon which substrate binding was affected. Overall, these data provide new insight into the mechanisms of tumor suppression by B56γ. IMPLICATIONS: This study further indicates the importance of B56γ-PP2A in tumorigenesis