Abnormal restriction pattern of PIP gene associated with human primary prostate cancers

A functional and regulatory network associated with PIP expression in human breast cancer

BACKGROUND

The PIP (prolactin-inducible protein) gene has been shown to be expressed in breast cancers, with contradictory results concerning its implication. As both the physiological role and the molecular pathways in which PIP is involved are poorly understood, we conducted combined gene expression profiling and network analysis studies on selected breast cancer cell lines presenting distinct PIP expression levels and hormonal receptor status, to explore the functional and regulatory network of PIP co-modulated genes.

PRINCIPAL FINDINGS

Microarray analysis allowed identification of genes co-modulated with PIP independently of modulations resulting from hormonal treatment or cell line heterogeneity. Relevant clusters of genes that can discriminate between [PIP+] and [PIP-] cells were identified. Functional and regulatory network analyses based on a knowledge database revealed a master network of PIP co-modulated genes, including many interconnecting oncogenes and tumor suppressor genes, half of which were detected as differentially expressed through high-precision measurements. The network identified appears associated with an inhibition of proliferation coupled with an increase of apoptosis and an enhancement of cell adhesion in breast cancer cell lines, and contains many genes with a STAT5 regulatory motif in their promoters.

CONCLUSIONS

Our global exploratory approach identified biological pathways modulated along with PIP expression, providing further support for its good prognostic value of disease-free survival in breast cancer. Moreover, our data pointed to the importance of a regulatory subnetwork associated with PIP expression in which STAT5 appears as a potential transcriptional regulator.

Chromosomal instability in oral cancer cells

Chromosomal instability is a common feature of human tumors, including oral cancer. Although a tumor karyotype may remain quite stable over time, chromosomal instability can lead to 'variations on a theme' of a clonal cell population, often with each cell within a tumor possessing a different karyotype. Thus, chromosomal instability appears to be an important acquired feature of tumor cells, since propagation of such a diverse cell population may facilitate evasion of standard therapies. There are several sources of chromosomal instability, although the primary causes appear to be defects in chromosomal segregation, telomere stability, cell-cycle checkpoint regulation, and the repair of DNA damage. Our understanding of the biological basis of chromosomal instability in cancer cells is increasing rapidly, and we are finding that the seemingly unrelated origins of this phenomenon may actually be related through the complex network of cellular signaling pathways. Here, we review the general causes of chromosomal instability in human tumors. Specifically, we address the state of our knowledge regarding chromosomal instability in oral cancer, and discuss various mechanisms that enhance the ability of cancer cells within a tumor to express heterogeneous karyotypes. In addition, we discuss the clinical relevance of factors associated with chromosomal instability as they relate to tumor prognosis and therapy.

Expression of the prolactin-inducible protein (PIP/GCDFP15) gene in benign epithelium and adenocarcinoma of the prostate

Prolactin-inducible protein (PIP), also known as gross cystic disease fluid protein 15, is a predominant secretory protein in various body fluids, including saliva, milk and seminal plasma. Immunohistochemistry of this protein has been exploited as a clinical marker for breast cancer and Paget's disease. This study comparatively examined PIP expression in normal prostate tissues and in adenocarcinomas of the prostate. Quantitative real-time RT-PCR revealed low-level presence (6%) of PIP mRNA in normal prostate tissue in comparison with the seminal vesicle. Indirect immunostaining with monoclonal antibody 3E7 displayed a positive sign for benign epithelium in 8 cases (29.6%) among 27 normal specimens; however, the incidence significantly increased to 56.1% (37/66) in instances involving primary prostate carcinoma tissues of different types. Quantitative RT-PCR also demonstrated that PIP transcript levels in carcinoma regions were significantly higher than corresponding levels in benign regions. These findings conclusively showed that benign prostate epithelium expresses PIP at low levels; in contrast, PIP is over-expressed in carcinomas of the prostate.

Expression of the mouse homologue for the human GCDFP-15/PIP gene during pre- and early post-natal development

The function of the mouse submaxillary gland/prolactin inducible protein (mSMGP/mPIP), the homologue of the human gross cystic disease fluid protein 15 (GCDFP-15)/prolactin inducible protein (hPIP) remains unknown. The human gene, normally expressed in apocrine glands of healthy individuals, is aberrantly expressed in human breast cancers where it is regulated by hormones including androgens, and in prostate cancers. We have previously reported that in the adult mouse and rat, gene expression is tissue-specific for the salivary and lacrimal glands, and is hormonally regulated. In this study, we examine the endogenous pattern of mouse SMGP/PIP (mSMGP/mPIP) gene expression in mid- and late-embryonic, and in early postnatal development. Gene expression was analyzed by RT-PCR followed by Southern blot analysis, and by in situ hybridization. Gene expression was detected in the submandibular gland as early as embryonic day 14 (E14), a period that coincides with the initiation of submandibular gland development in the embryo, suggesting that mSMGP/mPIP may have a functional role in the developing gland. Nearing the end of gestation, E18, mSMGP/mPIP transcripts were localized in the proacinar cells of the gland, and gene expression continued to be maintained following birth. In addition, during early postnatal development, mSMGP/mPIP gene expression was detected in the other two major salivary glands, the sublingual and parotid, as well as in the lacrimal gland and in reproductive tissues. In the prostate, gene expression was turned off by 10 weeks of age. The spatial and temporal pattern of the mSMGP/mPIP gene expression, in addition to our recent demonstration that mSMGP/mPIP is found in mouse saliva and can bind bacteria, suggest that this protein may have a protective role in the mouse.

Intragenic amplification and formation of extrachromosomal small circular DNA molecules from the PIP gene on chromosome 7 in primary breast carcinomas

The PIP gene is expressed in exocrine glands and, in pathologic conditions, in breast cysts and breast cancers exhibiting apocrine features. It is localized on the long arm of chromosome 7, a region frequently alterated in mammary tumors. We previously described an abnormal restriction pattern of the PIP gene in 33% of prostate carcinomas analyzed. Here, we analyze the structure of the PIP gene in primary breast carcinomas. We report that part of the 3' end, including exon 3, intron C, two-thirds of exon 4 and a small portion of intron B, is amplified and involved in the formation of extrachromosomal spcDNA molecules in 3/14 (21.4%) breast cancers analyzed. The involvement of a well-defined intragenic region of a gene in the formation of spcDNA appears to be unprecedented. Since spcDNA has been suggested to serve as an enhancer of genetic instability, the PIP gene may be the target of genomic variability processes in breast cancer.