Breast Cancer: Search of Hidden Culprits

To the Editor: Breast cancer globally outscores every other disease in female mortality. The major thrust for a cure remains confined to conventional drugs and radiation therapies with obvious shortcomings or fall outs. A logical first step for the development of effective genetic therapies is the identification of the breast cancer-associated genes. Although many genes are already associated, the list is not exhaustive by any means. In our quest for more genes associated with breast cancer we focused on intermediate filament (IF) as different studies have highlighted that some IFs are expressed in various malignancies including breast cancer (1). Additionally, its largest subgroup Cytokeratins (CKs), can be detected in serum from cancer patients and are widely used as tumor markers. Eleven IFs Cytokeratin (CK)1, CK3, CK4, CK9, CK10, CK12, CK13, CK23, Neurofilament H (NEFH), Desmuslin (DMN), and Filensin, judgmentally considered promising for association with breast cancer but not hitherto associated with it, were selected. Combination of restricted fragment differential display-polymerase chain reaction (RFDD-PCR), reverse transcriptase (RT-PCR), and semiquantitative RT-PCR were used to study their differential expression in normal, benign, and malignant breast tissues and results were compared with those for CK19 with an established breast cancer role (2). CK10 and CK13 were further investigated at protein level. Combination of restricted fragment differential display-polymerase chain reaction technique which has been professed to be a strong approach for the identification of expressed genes was used first. After RTPCR, undetected CK1, CK3, CK4, CK9, and weakly expressing CK13 were construed to be not expressing in breast. The weak expression of CK13 was reconfirmed via IMH at protein level also. Earlier studies had also highlighted the same weak expression for CK13 in breast cancer (3). Conversely, the remaining six genes amplified quite well and differentially expressed in three tissue types during semi-quantitative RT-PCR. Expression of CK10 is related to maturation of malignant keratinocytes, being preferentially detected in more differentiated parts. Besides being associated with tumors of other organs, it has also been suggested to be useful for grading carcinomas of the cervix (4). Previous study on CK10 had ruled out its association with breast cancer (5). We found it had significant expression in tumor tissues. To reconcile the difference in findings between our study and those of Bratthauer et al. (5), we subjected CK10 to IMH and found it strongly detected at protein level also. CK12 co-expresses with CK14 in cornea. CK14 has an established role in cancers of various organs including breast (6). We suspected that its corneal co-expressing partner might also be associated and found it expressing with significant upregulation in cancer tissues. Its association with any cancer was not established earlier. CK23 is a relatively new addition to the IF family. Until now, it was only associated with cancer of the pancreas (7). Zhang et al. (7) who closely related it to P21 also observed that in pancreatic cell lines P21 mediates CK23 and antisense P21 RNA also blocks the induction of CK23. CK23 being closely related to P21 was suspected for a similar role. We found it expressing in normal tissues 70% of the time, and the expression frequency increased in case of tumor tissues. Furthermore, compared with normal tissues CK23 was upregulated in cancer tissues and downregulated in benign ones. Mizuno et al. (8) found that colocalization of some IFs such as DMN and Desmin. Desmin has an established role in breast cancer (9). We therefore included DMN in our study and found it highly expressed in benign tissues and upregulated in tumor tissues as compared with normal ones. Address correspondence and reprint requests to: Saima Naz, Department of Anatomy, School of Preclinical & Forensic Medicine, Sichuan University, Cheng Du, Sichuan 610041, China, or E-mail: saimasaad2010@ yahoo.com.