Breast Cancer Tumor Suppressors: a Special Emphasis on Novel Protein Nischarin Mazvita Maziveyi and Suresh K
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Published OnlineFirst September 21, 2015; DOI: 10.1158/0008-5472.CAN-15-1395 Cancer Review Research Breast Cancer Tumor Suppressors: A Special Emphasis on Novel Protein Nischarin Mazvita Maziveyi and Suresh K. Alahari Abstract Tumor suppressor genes regulate cell growth and prevent vast number of cellular processes, including neuronal protection spontaneous proliferation that could lead to aberrant tissue and hypotension. The NISCH promoter experiences hypermethy- function. Deletions and mutations of these genes typically lead lation in several cancers, whereas some highly aggressive breast to progression through the cell-cycle checkpoints, as well as cancer cells exhibit genomic loss of the NISCH locus. Further- increased cell migration. Studies of these proteins are important more, we discuss data illustrating a novel role of Nischarin as as they may provide potential treatments for breast cancers. In this a tumor suppressor in breast cancer. Analysis of this new para- review, we discuss a comprehensive overview on Nischarin, a digm may shed light on various clinical questions. Finally, the novel protein discovered by our laboratory. Nischarin, or imida- therapeutic potential of Nischarin is discussed. Cancer Res; 75(20); zoline receptor antisera-selected protein, is a protein involved in a 4252–9. Ó2015 AACR. Introduction (6, 7). It also interacts with LIM kinase (LIMK) in order to prevent cytoskeletal reorganization (8). Typically, scaffold proteins such Breast cancer initiation and progression involve several genetic as Nischarin are characterized as caretaker genes because their events that can activate oncogenes and/or abrogate the function of effects on tumor growth are indirect. tumor suppressor genes. Tumor suppressor genes are commonly lost or deleted in cancers, facilitating the initiation and progres- sion of cancer through several biological events, including cell Discovery of Nischarin proliferation, cell death, cell migration, and cell invasion. Usually, The first function attributed to Nischarin was its role as an cancer mortality occurs due to complications of metastasis rather integrin a5b1 binding protein (9). In this way, Nischarin is able to than the mass effect of the primary tumor, and several tumor regulate cell motility, specifically by anatomization of cell signal- suppressors regulate metastasis. Genetic modifications through ing proteins that contribute to tumor cell migration and invasion allelic loss are one of the important factors for deregulation of (10). The structural and functional domains of Nischarin promote tumor suppressor genes. Importantly, promoter hypermethyla- its interaction with 17 known proteins to influence cell adhesion, tion of several tumor suppressors has been shown to be associated cell migration, vesicle trafficking, apoptosis, glucose metabolism, with tumor progression. In addition, several signaling mechan- and cell signaling. Thus far, diseases associated with the NISCH isms are dysregulated in breast cancer as a result of mutations in gene include hypertension, xerostomia, morphine dependence, these genes. Among the tumor suppressors, BRCA1/2, p53, PTEN, depression, anxiety, ventricular hypertrophy, congestive heart ATM, Rb, LKB, Nm23, and p16 have been studied in great detail failure, rosacea, several cancers (11). Its location at 3p21.1 puts and discussed in many review articles (1–3). This article primarily it in a category of tumor suppressor genes that are associated with emphasizes the novel tumor suppressor Nischarin (Fig. 1) and the development of many cancers (12). Highly aggressive breast how it regulates cell migration, cell invasion, tumor growth, and cancer cells frequently exhibit genomic loss of the NISCH locus metastasis through various signaling pathways and interactions (12), whereas the NISCH promoter is hypermethylated in lung with other proteins. Caretaker genes, such as BRCA1, are genes cancers (13). Nischarin mRNA and protein expression is high in whose loss does not directly inhibit tumor growth (1, 4, 5). stage 0 human breast specimens but reduced in stage I–IV breast Nischarin imposes its tumor-suppressive functions through its cancer specimens (12). interactions with other proteins; thus, it is a caretaker tumor suppressor gene. For example, it interacts with p21 activated kinase 1 (PAK1) and integrin a5 to prevent cell migration NISCH Regulation The structural and functional domains of Nischarin Nischarin was first characterized 15 years ago by SK Alahari Department of Biochemistry and Molecular Biology, Louisiana State and colleagues (10). The 37,955 bases of the full-length NISCH University Health Sciences Center, New Orleans, Louisiana. gene are regulated by the transcription factors max1, sp1, Corresponding Author: Suresh K. Alahari, Louisiana State University Health COUP, olf-1, COUP-TF, pax-4a, ATF, and c-Myc (11). Soon Sciences Center, 1901 Perdido Street, New Orleans, LA 70112. Phone: 504-568- after, the human homolog of Nischarin was discovered as 4734; Fax: 504-568-2093; E-mail: [email protected] imidazoline receptor antisera-selected protein (IRAS; ref. 14). doi: 10.1158/0008-5472.CAN-15-1395 Human IRAS has 80% homology with rodent Nischarin but Ó2015 American Association for Cancer Research. interestingly, the integrin a5-binding sites of Nischarin and 4252 Cancer Res; 75(20) October 15, 2015 Downloaded from cancerres.aacrjournals.org on September 27, 2021. © 2015 American Association for Cancer Research. Published OnlineFirst September 21, 2015; DOI: 10.1158/0008-5472.CAN-15-1395 Tumor Suppressor Nischarin Rac1 Rac1 PAK1 LIMK Rab 14 LKB1 IRS 1–4 PI3P PI3P Coiled- Coil Alanine/ PX Leucine-Rich repeats Integrin Binding proline NH2 Glutamine COOH rich rich 1 300 600 900 1504 Serine phosphorylation Ubiquitination Tyrosine phosphorylation Acetylation Threonine phosphorylation © 2015 American Association for Cancer Research Figure 1. The predicted post-translational modifications of Nischarin. Ubiquitination of Nischarin is predicted to occur at K1009, K1015, K1290, K1299, and K1303. Acetylation is predicted to occur at K1015. The predicted human Nischarin phosphorylation sites are S246, S250, T252, S477, S541, S546, S883, S1022, S1038, T1282, S1284, Y1293, Y1294, and Y1307. Both Nischarin's PX domain, and its coiled-coil domain are essential for endosomal targeting and interaction with phosphatidylinositol 3-phosphate (PI3P) in PI3P-enriched endosomes. Amino acids 1–624 of Nischarin strongly interact with p21-activated kinase 1 (PAK1). LKB1 interacts with positions 416–624 of Nischarin. Insulin receptor substrates 1–4 interact with the C-terminal domain of Nischarin. Positions 416–624 of Nischarin are sufficient to interact with LIMK. Residues 464 to 562 of Nischarin interact with the integrin a5 cytoplasmic tail. Rab14 interacts with Nischarin's C-terminus. Both the N- and C-terminus of Nischarin interact with Rac1. IRASare100%identical(Fig.2;ref.14).Inhumans,Nischarin/ 516, as well as amino acids 517–1593 missing (17). Isoform 7 IRAS was first discovered as an I1-imidazoline receptor, which has a long amino acid sequence difference between 122–153 are expressed in both neurons and astrocytes (14, 15). Human and amino acids 143–1593 missing (17). and mouse Nischarin differ in the alanine/proline rich region, Furthermore, the N-terminus of Nischarin contains a phox which is removed in human Nischarin (Fig. 2). (PX) domain from amino acids 11–121 (Fig. 1; ref. 18). This Nischarin is a cytosolic protein that anchors itself to the inner PX domain is necessary for plasma membrane and vesicular layer of the plasma membrane and has been found to interact targeting of Nischarin (19). Both Nischarin's PX domain, and with both cytosolic and intermembrane proteins (16). Human its coiled-coil domain (634–695) are essential for endosomal Nischarin has four isoforms that are achieved by alternative targeting and interaction with phosphatidylinositol 3-phosphate splicing (9). Isoform 1 encodes the full-length protein and is PI3P in endosomes enriched in this phospholipid (Fig. 1; ref. 19). highly expressed in neural and endocrine tissue (Fig. 2; ref. 9). Though the interaction of PI3P and Nischarin alone is not Isoform 2 has amino acids 1–511 spliced and is expressed in sufficient for endosomal targeting, this interaction occurs around the brain (9). Isoform 3, also known as IRAS-L, is highly region 2–133 of Nischarin. Although regions 120–695 are nec- expressed in the brain, missing amino acids 584–1504, and essary for Nischarin to be targeted to the endosomes, mutation of has a modified sequence in amino acids 511–583 (9). Isoform amino acids 49 and 50 inhibit endosomal targeting (18). 4, also known as IRAS-S, is also highly expressed in the brain, Interestingly, other regions of Nischarin have been found to has amino acids 516–1504 spliced out, and has a change in interact with other signaling molecules as well. For example, amino acids between 512 and 515 (9). Isoform 1 is 166,629 amino acids 1–624 of Nischarin have been found to strongly Da, isoform 2 is 110,194 Da, isoform 3 is 63,997 Da, and interact with p21 activated kinase 1 (PAK1) to prevent cell isoform 4 is 56,867 Da (9). migration (Fig. 1; ref. 6). Positions 416–624 of Nischarin are Mouse Nischarin has seven isoforms that are achieved by sufficient to interact with LIMK in order to prevent cytoskeletal alternative splicing (Fig. 2; ref. 17). Isoform 1 is full-length reorganization (Fig. 1; ref. 8). LKB1 interacts with positions 416– Nischarin, which is 1,593 amino acids (17). Isoform 2 is 624 of Nischarin to prevent cancer progression (Fig. 1; ref. 20). In missing amino acids 348–500 and isoform 3 is missing amino addition, Rab14 and insulin receptor substrates 1–4 interact with acids 1–245 (17). Amino acids 437–472 of isoform 4 differ the c-terminal domain of Nischarin (Fig. 1; refs. 21, 22). Among from the canonical sequence and it is also missing amino acids the known binding partners of Nischarin, its interaction with 473–1593 (17). Amino acids 332–334 of isoform 5 have a integrin a5 is the best characterized. sequence difference and amino acids 335–1593 are missing Integrins are cell adhesion proteins with a and b transmem- (17).