Bcl-2, bax, bcl-xL and bcl-xS expression in neoplastic and normal cervical tissue
Introduction
Besides bcl-2, the first protein to be identified with anti-apoptotic potential [1], the bcl-2 family includes a number of proteins with either agonistic or antagonistic activity on bcl-2, whose relative amounts and interactions determine cellular susceptibility to programmed cell death [2]. Among the best characterized proteins of this family are bax and bcl-x, with bcl-x possessing two different splicing isoforms, bcl-xL (long) which interacts with bcl-2 to inhibit programmed cell death and bcl-xS, (short) which acts, similarly with bax, in pro-apoptotic activities [3], [4].
The involvement of the bcl-2 family in neoplastic transformation has been recently investigated in different cellular systems: overexpression of bcl-2 contributes to the clonal growth of cancer cells and seems to affect the occurrence of metastases by rendering cells resistant to cell death induced by loss of attachment to extracellular matrix proteins [5], [6].
Several studies have been performed to assess the role of alterations of bcl-2 family members in various malignancies: increased bcl-2 expression has been found in hematopoietic and solid tumors [7], [8], [9], [10] and has been generally associated with a more favorable clinical outcome.
Moreover, bcl-2 overexpression protects cancer cells from apoptotic cell death induced by a variety of stimuli, including radiation and most cytotoxic drugs, thus interfering with the response to therapeutic interventions [11], [12]. Similarly, the presence of bax has been demonstrated to be associated with restoring the sensitivity to apoptotic stimuli and to radiation in breast cancer cells [13], and with a better chance of response to chemotherapy in human breast cancer [14].
The involvement of bcl-2 in the progression from cervical intraepithelial neoplasias (CIN) to invasive cervical cancer has also been described [15], [16], [17] and it has been reported that modulation of bcl-2 and/or bax is associated with radiotherapy and chemotherapy induced apoptosis in cervical carcinoma [18], [19], [20], [21].
Given the reciprocal and complex interactions of bcl-2 and related proteins in regulating apoptosis and susceptibility to treatment, it is conceivable that the simultaneous assessment of several members of this still growing family could provide a more thorough understanding of the role of apoptosis in the biology of cervical carcinoma.
The aim of this study was to simultaneously measure the protein expression levels of bcl-2, bax, bcl-xL and bcl-xS in a series of normal and neoplastic cervical tissue samples and to analyze for any correlation with clinico-pathological parameters. Moreover, the association of these proteins with susceptibility to chemotherapy and survival has also been investigated.
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Patients and sample collection
This study was performed on 68 cervical tissue samples, which included 53 cervical cancers and 15 normal samples. All patients were enrolled from October 1994 to January 1997 at the Department of Obstetrics and Gynecology of the Catholic University in Rome. Normal cervical tissue specimens were obtained from hysterectomy performed for benign conditions in 15 patients (median age 47 years; range 38–72 years). Ten patients were pre-menopausal, while five cases were post-menopausal.
Cervical cancer
Results
Bcl-2, bax and bcl-x protein levels were measured by Western blotting on a total of 68 cervical samples, which included 53 cervical carcinomas and 15 normal tissues. A band of the expected molecular weight of 26 kDa for bcl-2, of 21 kDa for bax and of 30 kDa for bcl-xL was detected in all samples (Fig. 1). bcl-xS (18 kDa) was present at barely detectable levels in only 12 (20.3%) of the neoplastic samples analyzed and in none of the normal tissues. The two isoforms of bcl-x were evident in the
Discussion
Evidence is available about the possible involvement of the bcl-2 family in the natural history of cervical intraepithelial neoplasia as well as in invasive cervical cancer [7], [15], [16], [17]. However, the assessment of a single member of this family, characterized by the coexistence and interaction of various proteins with opposite functions, may provide only limited information. In this report, the simultaneous evaluation of bcl-2, bax, bcl-xL and bcl-xS protein levels has been performed
Acknowledgements
This work was partially supported by Associazione Italiana per la Ricerca sul Cancro (A.I.R.C.).
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