Using a new subtraction method and chemically induced rat hepatocellular carcinomas, we identified a hepatocellular carcinogenesis and hepatocyte proliferation- related gene designated hp33 that encoded a 33-kDa protein. The predicted protein was similar to the bovine aralkyl

The regulatory mechanism of ordered cell proliferation and cell cycle progression of eukaryotes is a current central subject in cell biology. The identification of factors related to this mechanism is most critical to an understanding of the above cellular behaviors, and many functional molecules including kinases, phosphatases, cyclins and check point factors have been discovered so far. However, despite the uncovering of many regulatory factors related to cell proliferation, it is still unclear what the related input (signal-generating factors) and final output (effector apparatus) molecules are. The centrosome is the most typical cellular apparatus governing cell cycle progression. The centrosome functions as a major microtubule (MT) organizing center (MTOC) of interphase and mitotic cells. The mammalian centrosome consists of a centriole and pericentriolar matrix (PCM) (Lange and Gull, 1996). The centrosome is the nucleus of MT arrays that provide a wide variety of cellular processes, including the mechanical scaffolds of a cell, rails for vesicle transport and mitotic apparatus (Kellogg et al., 1994). Many kinds of structural proteins, MT-based motor proteins, microtubule-associated proteins (MAPs) and their regulatory factors were found to be related to centrosome/MT-systems (Paoletti and Bornens, 1997). Their ability to participate in centrosome/MT organization has been well characterized in cell-free systems and by mutation analysis. However, except for the conventional MAPs observed in nervous systems and centrosomal protein identified from the analysis of Drosophila mutants (Gonzalez et al., 1998; Kobayashi and Mundel, 1998), little is known about centrosomal proteins and MAPs, especially their relationship to cell proliferation and tissue differentiation. We have been searching for molecules related to cell growth and carcinogenesis in the rat liver. The rat liver has several 1353 Journal of Cell Science 112, 1353-1364 (1999) Printed in Great Britain © The Company of Biologists Limited 1999 JCS4662