Bcl-2 exerts a pRb-mediated cell cycle inhibitory function in HEC1B endometrial carcinoma cells.
OBJECTIVE
In various human tumors the expression of Bcl-2 appears to vary significantly during the transformation process. Indeed, in several glandular systems, Bcl-2 levels appear to be sustained in premalignant lesions and rather low after the malignant change. Since we recently reported that transformed human endometrial cells display constitutively low levels of Bcl-2, we set out to investigate the biological meaning of this down-regulation. To this end we analyzed the effects of Bcl-2 forced overexpression in a moderately differentiated endometrial cell line of human origin.


METHODS
Bcl-2 overexpression was obtained by transfecting HEC1B human endometrial adenocarcinoma cells with a suitable bcl-2 vector. The effects of Bcl-2 overepression were evaluated in several transfectants (cell clones and mixed populations) by FACS, growth rates, cloning efficiencies, and modification of the phosphorylation status of the pRb protein. Accompanying changes in the expression of the CDK inhibitor p21(WAF1/CIP1) were evaluated as well.


RESULTS
Bcl-2 overexpression resulted in a reduced cell proliferation rate, decreased cloning efficiency, appreciable cell morphology changes, G2/M cell cycle arrest, remarkable accumulation of the dephosphorylated form of retinoblastoma protein, and a significant rise in p21(WAF1/CIP1).


CONCLUSIONS
From these observation it may be deduced that the observed loss and down-regulation of the antiapoptotic protein in endometrial glandular human tumors is not random but possibly related to the cellular transformation process. It may be also inferred that the coincidence of a progressive fading of both Bcl-2 and cyclin inhibitor p21(WAF1/CIP1) expressions, together with accumulation of the hyperphosphorylated form of the retinoblastoma protein, may be seen as a potential indicator of ongoing malignant changes.
Crescenzi
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Dipartimento di Biologia e Patologia Cellulare e Molecolare L. Califano, Università di Napoli Federico II, 80131 Naples, Italy.
Palumbo
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D000230:Adenocarcinoma / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D000970:Antineoplastic Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects; D002453:Cell Cycle / Q000235:genetics / Q000502:physiology*; D002455:Cell Division / Q000502:physiology; D002461:Cell Line, Transformed; D002945:Cisplatin / Q000494:pharmacology; D004261:DNA Replication / Q000502:physiology; D004273:DNA, Neoplasm / Q000096:biosynthesis; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm; D016889:Endometrial Neoplasms / Q000235:genetics / Q000378:metabolism / Q000473:pathology*; D005260:Female; D015972:Gene Expression Regulation, Neoplastic; D019254:Genes, bcl-2; D006801:Humans; D010766:Phosphorylation; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology*; D016160:Retinoblastoma Protein / Q000378:metabolism / Q000502:physiology*; D014162:Transfection
D000970:Antineoplastic Agents; D004273:DNA, Neoplasm; D019253:Proto-Oncogene Proteins c-bcl-2; D016160:Retinoblastoma Protein; D002945:Cisplatin