Yoh Dobashi

Involvement of Cyclins in Cell Proliferation and Their Clinical Implications in Soft Tissue Smooth Muscle Tumors

Expression of cyclins A and E and cyclin-dependent kinase 2 (cdk2) was examined immunohistochemically in 55 cases of soft tissue smooth muscle tumors, including vascular leiomyoma, and compared to expression of Ki-67 and proliferating cell nuclear antigen. Cyclin A was expressed in 70% of the leiomyoma cases, but with much lower labeling indexes than in leiomyosarcoma. Cyclin E was expressed exclusively in leiomyosarcoma. Although the differences of cyclin A- and cyclin E-labeling indexes between leiomyoma and leiomyosarcoma were statistically significant, no significant differences were found in the other markers. Furthermore, cyclin A- and/or E-positivity predicted a poor prognosis in recurrence- or metastasis-free survivals and overall survival. Immunoblotting revealed that cyclins A and E were expressed, in complex with cdk2, exclusively in tumors. In addition, not only leiomyosarcoma, but also leiomyoma specimens that exhibited negligible levels of complex expression, manifested detectable cdk2 activity. These results suggest 1) up-regulation of active cyclin A/cdk2 expression and associated kinase activity is critical for unrestrained cell proliferation; 2) cyclin E/cdk2 complexes may play a crucial role in leiomyosarcoma; 3) immunohistochemical detection of cyclins can be a more reliable tool for differential diagnosis between leiomyoma versus leiomyosarcoma than that of Ki-67 or proliferating cell nuclear antigen, and be a possible prognostic indicator.

Diversity in expression and prognostic significance of G1/S cyclins in human primary lung carcinomas

Expression of cyclin A, cyclin E and cdk2 was examined immunohistochemically in 144 cases of primary non‐small cell lung carcinoma to evaluate their prognostic value. Cyclin A was co‐expressed with cdk2 in the proliferating cells, ie those showing positive Ki‐67 staining. The labelling index (LI) of cyclin A revealed a positive correlation with the S‐phase fraction and an inverse correlation with histological differentiation. Furthermore, high cyclin A LIs indicated a poor prognosis in all histological types. Cyclin E exhibited a characteristic staining pattern: in squamous cell carcinoma (SCC), differentiated cells without Ki‐67 staining revealed cyclin E positivity with expression of cdk2. Conversely, in adenocarcinoma (AC), proliferating cells revealed cyclin E positivity. Cases of large cell carcinoma showed heterogeneous cyclin E staining patterns, unlike those of SCC or AC. Statistical analyses also revealed a marked contrast between SCC and AC. In AC, the LI of cyclin E was inversely correlated with histological differentiation and a high LI predicted a worse prognosis. In contrast, in SCC, the LI of cyclin E correlated positively with histological differentiation and better prognosis. However, the expression levels of cyclin E mRNA evaluated by quantitative RT‐PCR were higher in poorly differentiated SCC and AC, suggesting that protein turnover plays a large role in determining cyclin E protein levels. Although the expression of cyclins was demonstrated to be diversely regulated depending on the histological type, the combined immunohistochemical analyses performed in this study on these proteins could be useful tools for evaluating patient prognosis in lung carcinomas. Copyright

Tumor Extension and Cell Proliferation in Adenocarcinomas of the Lung

To elucidate the mechanism of tumor extension in human pulmonary adenocarcinoma, we immunohistochemically investigated the expression of cell cycle regulator proteins in 54 small adenocarcinomas less than 3 cm in diameter. The Ki-67-labeling index was significantly higher in the periphery of the tumor nodule than in the center. This proliferative potential correlated well with coexpression of cdk2 and cyclin A. p27, one of the cdk inhibitors, was highly expressed in normal bronchial epithelial cells. Peripherally located tumor cells expressed p27 at an intermediate level, but at a higher frequency and level than those in the center. Expression of p21 was also predominant in the periphery. Furthermore, the expression patterns of p21 and p27 were reciprocal. In vitro kinase assays further demonstrated higher cdk2 kinase activity in the periphery. These results suggest that: (i) within an emerging extension made up of peripherally located tumor cells, their high proliferative potential gradually wanes as their relative topographical position becomes more central in the expanding tumor; (ii) peripherally located tumor cells maintain their proliferative potential by higher cyclin A-cdk2 complex activity; and (iii) intermediate expression of p21/p27 in the peripherally located cells promotes higher cyclin A-cdk2 kinase activity, whereas high p21/p27 expression in nonneoplastic cells inhibits kinase activity.

Overexpression of cdk4/cyclin D1 induces apoptosis in PC12 cells in the presence of trophic support

The induction of apoptosis by cell cycle regulator molecules under conditions optimal for exponential growth was examined in rat pheochromocytoma PC12 cells by overexpression of cyclins and cyclin‐dependent kinases (cdks). By flow cytometry and by immunofluorescence, only cells overexpressing cdk4 or cyclin D1 underwent apoptosis, which was not associated with G1‐arrest. Cdk4 kinase activity was significantly higher in cdk4‐, or cyclin D1‐expressing cells. Furthermore, induction of apoptosis by cdk4 was abrogated by co‐transfection of p16INK4, or dominant negative cdk4. These results suggest that upregulation of cdk4 kinase activity is a primary and critical mediator of apoptosis in PC12 cells under physiological conditions.

Combined clear and granular cell leiomyoma of soft tissue: evidence of transformation to a histiocytic phenotype

We present an unusual case of leiomyoma with a clear and granular cell pattern in which there was immunohistochemical evidence of transformation to a histiocytic phenotype.