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Prolactin-induced protein (PIP)-characterization and role in breast cancer progression.

ABSTRACT: Prolactin-induced protein (PIP) is a small secreted glycoprotein carrying several N-linked carbohydrate chains. The expression of PIP is generally restricted to cells with apocrine properties. It was found in apocrine glands of the axilla, vulva, eyelid, ear canal, and seminal vesicle. Being a secretory protein, PIP is present in seminal plasma, saliva, lacrimal fluid, tears, sweat gland secretion. Little is known about the biological role of PIP. It binds to numerous proteins, however, in most cases the biological role of such interactions is poorly understood. A notable exception is its binding to CD4 receptors present on the surface of T lymphocytes, macrophages, and spermatozoa. The available data suggest that PIP can have immunomodulatory functions and plays an important role in cell-mediate adoptive immunity. PIP binds to bacteria from several genera, which suggests that this glycoprotein may participate also in innate immunity and protection of hosts against microbial infections. Increased levels of PIP were found in several types of human cancer (prostate, sweat and salivary gland cancers). It is especially common in breast cancer, however, data on the expression of PIP in normal and cancerous breast cancer tissues are to some degree conflicting. In early studies, it was shown that PIP is absent or its expression is very low in normal breast epithelium, whereas in breast cancers PIP is frequently expressed and present in large amounts. On the other hand, later study showed that expression of PIP is lower in advanced apocrine carcinomas and invasive carcinomas than in, respectively, in situ carcinomas and adjacent normal tissue. The most recent study revealed that PIP gene expression decreased gradually along with higher stage and grade of breast cancer. In agreement with these data, it was shown that that low levels or the lack of PIP expression are associated with a worse response of breast cancer cells to chemotherapy. It was proposed that PIP plays important role in the development and progression of breast cancer. However, its role in these processes is both unclear and controversial. In this review, the role of PIP in both physiological processes and carcinogenesis is discussed.

SUBMITTER: Urbaniak A

PROVIDER: S-EPMC6291655 | biostudies-other | 2018

REPOSITORIES: biostudies-other

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Project description:Molecular apocrine is a subtype of estrogen receptor (ER)-negative breast cancer that is characterized by a steroid-response gene signature. We have recently identified a positive feedback loop between androgen receptor (AR) and extracellular signal-regulated kinase (ERK) signaling in this subtype. In this study, we investigated the transcriptional regulation of molecular apocrine genes by the AR-ERK feedback loop.The transcriptional effects of AR and ERK inhibition on molecular apocrine genes were assessed in cell lines. The most regulated gene in this process, prolactin-induced protein (PIP), was further studied using immunohistochemistry of breast tumors and xenograft models. The transcriptional regulation of PIP was assessed by luciferase reporter assay and chromatin immunoprecipitation. The functional significance of PIP in cell invasion and viability was assessed using siRNA knockdown experiments and the mechanism of PIP effect on integrin-?1 signaling was studied using immunoblotting and immunoprecipitation.We found that PIP is the most regulated molecular apocrine gene by the AR-ERK feedback loop and is overexpressed in ER-/AR+ breast tumors. In addition, PIP expression is regulated by AR-ERK signaling in xenograft models. These observations are explained by the fact that PIP is a target gene of the ERK-CREB1 pathway and is also induced by AR activation. Furthermore, we demonstrated that PIP has a significant functional role in maintaining cell invasion and viability of molecular apocrine cells because of a positive regulatory effect on the Integrin-ERK and Integrin-Akt signaling pathways. In fact, PIP-knockdown markedly decreases the phosphorylation of ERK, Akt, and CREB1. Importantly, PIP knockdown leads to a marked reduction of integrin-?1 binding to ILK1 and ErbB2 that can be reversed by the addition of fibronectin fragments.We have identified a novel feedback loop between PIP and CREB1 mediated through the Integrin signaling pathway. In this process, PIP cleaves fibronectin to release fragments that activate integrin signaling, which in turn increases PIP expression through the ERK-CREB1 pathway. In addition, we demonstrated that PIP expression has a profound effect on cell invasion and the viability of molecular apocrine cells. Therefore, PIP signaling may be a potential therapeutic target in molecular apocrine breast cancer.

Project description:Tumors that express estrogen receptor alpha (ER?+) comprise 75% of breast cancers in women. While treatments directed against this receptor have successfully lowered mortality rates, many primary tumors initially or later exhibit resistance. The paucity of murine models of this "luminal" tumor subtype has hindered studies of factors that promote their pathogenesis and modulate responsiveness to estrogen-directed therapeutics. Since epidemiologic studies closely link prolactin and the development of ER?+ tumors in women, we examined characteristics of the aggressive ER?+ and ER?- carcinomas which develop in response to mammary prolactin in a murine transgenic model (neu-related lipocalin- prolactin (NRL-PRL)). To evaluate their relationship to clinical tumors, we determined phenotypic relationships among these carcinomas, other murine models of breast cancer, and features of luminal tumors in women.We examined a panel of prolactin-induced tumors for characteristics relevant to clinical tumors: histotype, ER?/progesterone receptor (PR) expression and estrogen responsiveness, Activating Protein 1 (AP-1) components, and phosphorylation of signal transducer and activator of transcription 5 (Stat5), extracellular signal regulated kinase (ERK) 1/2 and AKT. We compared levels of transcripts in the ER?-associated "luminal" signature that defines this subtype of tumors in women and transcripts enriched in various mammary epithelial lineages to other well-studied genetically modified murine models of breast cancer. Finally, we used microarray analyses to compare prolactin-induced ER?+ and ER?- tumors, and examined responsiveness to estrogen and the anti-estrogen, Faslodex, in vivo.Prolactin-induced carcinomas were markedly diverse with respect to histotype, ER?/PR expression, and activated signaling cascades. They constituted a heterogeneous, but distinct group of murine mammary tumors, with molecular features of the luminal subtype of human breast cancer. In contrast to morphologically normal and hyperplastic structures in NRL-PRL females, carcinomas were insensitive to ER?-mediated signals. These tumors were distinct from mouse mammary tumor virus (MMTV)-neu tumors, and contained elevated transcripts for factors associated with luminal/alveolar expansion and differentiation, suggesting that they arose from physiologic targets of prolactin. These features were shared by ER?+ and ER?- tumors, suggesting a common origin, although the former exhibited transcript profiles reflecting greater differentiation.Our studies demonstrate that prolactin can promote diverse carcinomas in mice, many of which resemble luminal breast cancers, providing a novel experimental model to examine the pathogenesis, progression and treatment responsiveness of this tumor subtype.

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Prolactin-induced protein (PIP)-characterization and role in breast cancer progression.

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