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細胞周期制御における分子シャペロン73kD熱ショック蛋白質の機能：鳥越俊彦¹，旗本恵介^1,2，石川雅子¹，平井到¹，田矢洋一³，澤田美智子⁴，金子正光²，佐藤昇志¹，菊地浩吉^1,5　（札幌医大・医・¹第１病理，²救急集中治療，³国立がんセ・生物，⁴北工研, ⁵札幌IDL ）

The function of 73 kD heat shock protein in the regulation of cell cycle：Toshihiko TORIGOE¹, Keisuke HATAMOTO^1,2, Masako ISHIKAWA¹, Itaru HIRAI¹, Yoichi TAYA³, Michiko SAWADA⁴, Masamitsu KANEKO², Noriyuki SATO¹, Kokichi KIKUCHI^1,5 (¹Dept. Pathol., ²Dept. Trauma and ICU, Sapporo Med. Univ. Sch. Med., ³Natl. Cancer Center Res. Inst., ⁴Hokkaido Natl. Ind. Res. Inst., ⁵Sapporo Immuno Diagnostic Lab.)

Retinoblastoma protein (pRb) has an important role in the cell cycle control as a negative regulator of G1/S transition. We have demonstrated that the dephosphorylated pRb was associated with 73 kD heat shock protein (HSC73), one of molecular chaperones which play roles for protein folding, assembly and sorting in mammarian cells. We determined the HSC73-binding region of pRb and analyzed a functional significance of the interaction. The presence of HSC73 rendered purified pRb detectable by native PAGE analysis, indicating that HSC73 could mediate the conformational change of pRb. This change was facilitated by the addition of HSP40, the co-chaperone of HSC73. Furthermore, it was revealed that the dephosphorylated pRb became resistant to the degradation by purified 20S proteasome in vitro in the presence of HSC73 and HSP40. Our data suggest that the molecular chaperone HSC73 functions as a protein stabilizer of dephosphorylated pRb, thus supporting the negative regulatory function of pRb in the cell cycle progression especially under stress conditions.