Use of a cryptic splice site for the expression of huntingtin interacting protein 1 in select normal and neoplastic tissues

Huntingtin interacting protein 1 (HIP1) is a 116-kDa endocytic protein, which is necessary for the maintenance of several tissues in vivo as its deficiency leads to degenerative adult phenotypes. HIP1 deficiency also inhibits prostate tumor progression in mice. To better understand how deficiency of HIP1 leads to such phenotypes, we analyzed tumorigenic potential in mice homozygous for a Hip1 mutant allele, designated Hip1(Delta 3-5), which is predicted to result in a frame-shifted, nonsense mutation in the NH(2) terminus of HIP1. In contrast to our previous studies using the Hip1 null allele, an inhibition of tumorigenesis was not observed as a result of the homozygosity of the nonsense Delta 3-5 allele. To further examine the contrasting results from the prior Hip1 mutant mice, we cultured tumor cells from homozygous Delta 3-5 allele-bearing mice and discovered the presence of a 110-kDa form of HIP1 in tumor cells. Upon sequencing of Hip1 DNA and message from these tumors, we determined that this 110-kDa form of HIP1 is the product of splicing of a cryptic U12-type AT-AC intron. This event results in the insertion of an AG dinucleotide between exons 2 and 6 and restoration of the reading frame. Remarkably, this mutant protein retains its capacity to bind lipids, clathrin, AP2, and epidermal growth factor receptor providing a possible explanation for why tumorigenesis was not altered after this knockout mutation. Our data show how knowledge of the transcript that is produced by a knockout allele can lead to discovery of novel types of molecular compensation at the level of splicing.

Aberrant Huntingtin interacting protein 1 in lymphoid malignancies

Huntingtin interacting protein 1 (HIP1) is an inositol lipid, clathrin, and actin binding protein that is overexpressed in a variety of epithelial malignancies. Here, we report for the first time that HIP1 is elevated in non-Hodgkin's and Hodgkin's lymphomas and that patients with lymphoid malignancies frequently had anti-HIP1 antibodies in their serum. Moreover, p53-deficient mice with B-cell lymphomas were 13 times more likely to have anti-HIP1 antibodies in their serum than control mice. Furthermore, transgenic overexpression of HIP1 was associated with the development of lymphoid neoplasms. The HIP1 protein was induced by activation of the nuclear factor-kappaB pathway, which is frequently activated in lymphoid malignancies. These data identify HIP1 as a new marker of lymphoid malignancies that contributes to the transformation of lymphoid cells in vivo.

Crystal structure at 2.8 A of Huntingtin-interacting protein 1 (HIP1) coiled-coil domain reveals a charged surface suitable for HIP1 protein interactor (HIPPI)

Huntington's disease is a genetic neurological disorder that is triggered by the dissociation of the huntingtin protein (htt) from its obligate interaction partner Huntingtin-interacting protein 1 (HIP1). The release of the huntingtin protein permits HIP1 protein interactor (HIPPI) to bind to its recognition site on HIP1 to form a HIPPI/HIP1 complex that recruits procaspase-8 to begin the process of apoptosis. The interaction module between HIPPI and HIP1 was predicted to resemble a death-effector domain. Our 2.8-A crystal structure of the HIP1 371-481 subfragment that includes F432 and K474, which is important for HIPPI binding, is not a death-effector domain but is a partially opened coiled coil. The HIP1 371-481 model reveals a basic surface that we hypothesize to be suitable for binding HIPPI. There is an opened region next to the putative HIPPI site that is highly negatively charged. The acidic residues in this region are highly conserved in HIP1 and a related protein, HIP1R, from different organisms but are not conserved in the yeast homologue of HIP1, sla2p. We have modeled approximately 85% of the coiled-coil domain by joining our new HIP1 371-481 structure to the HIP1 482-586 model (Protein Data Bank code: 2NO2). Finally, the middle of this coiled-coil domain may be intrinsically flexible and suggests a new interaction model where HIPPI binds to a U-shaped HIP1 molecule.

Degenerative phenotypes caused by the combined deficiency of murine HIP1 and HIP1r are rescued by human HIP1

The members of the huntingtin-interacting protein-1 (HIP1) family, HIP1 and HIP1-related (HIP1r), are multi-domain proteins that interact with inositol lipids, clathrin and actin. HIP1 is over-expressed in a variety of cancers and both HIP1 and HIP1r prolong the half-life of multiple growth factor receptors. To better understand the physiological importance of the HIP1 family in vivo, we have analyzed a large cohort of double Hip1/Hip1r knockout (DKO) mice. All DKO mice were dwarfed, afflicted with severe vertebral defects and died in early adulthood. These phenotypes were not observed during early adulthood in the single Hip1 or Hip1r knockouts, indicating that HIP1 and HIP1r compensate for one another. Despite the ability of HIP1 and HIP1r to modulate growth factor receptor levels when over-expressed, studies herein using DKO fibroblasts indicate that the HIP1 family is not necessary for endocytosis but is necessary for the maintenance of diverse adult tissues in vivo. To test if human HIP1 can function similar to mouse HIP1, transgenic mice with 'ubiquitous' expression of the human HIP1 cDNA were generated and crossed with DKO mice. Strikingly, the compound human HIP1 transgenic DKO mice were completely free from dwarfism and spinal defects. This successful rescue demonstrates that the human HIP1 protein shares some interchangeable functions with both HIP1 and HIP1r in vivo. In addition, we conclude that the degenerative phenotypes seen in the DKO mice are due mainly to HIP1 and HIP1r protein deficiency rather than altered expression of neighboring genes or disrupted intronic elements.

Huntingtin Interacting Protein 1 Is a Novel Brain Tumor Marker that Associates with Epidermal Growth Factor Receptor

Huntingtin interacting protein 1 (HIP1) is a multidomain oncoprotein whose expression correlates with increased epidermal growth factor receptor (EGFR) levels in certain tumors. For example, HIP1-transformed fibroblasts and HIP1-positive breast cancers have elevated EGFR protein levels. The combined association of HIP1 with huntingtin, the protein that is mutated in Huntington's disease, and the known overexpression of EGFR in glial brain tumors prompted us to explore HIP1 expression in a group of patients with different types of brain cancer. We report here that HIP1 is overexpressed with high frequency in brain cancers and that this overexpression correlates with EGFR and platelet-derived growth factor beta receptor expression. Furthermore, serum samples from patients with brain cancer contained anti-HIP1 antibodies more frequently than age-matched brain cancer-free controls. Finally, we report that HIP1 physically associates with EGFR and that this association is independent of the lipid, clathrin, and actin interacting domains of HIP1. These findings suggest that HIP1 may up-regulate or maintain EGFR overexpression in primary brain tumors by directly interacting with the receptor. This novel HIP1-EGFR interaction may work with or independent of HIP1 modulation of EGFR degradation via clathrin-mediated membrane trafficking pathways. Further investigation of HIP1 function in brain cancer biology and validation of its use as a prognostic or predictive brain tumor marker are now warranted.

Identification of Putative Androgen Receptor Interaction Protein Modules

We have developed a novel androgen receptor (AR) expression system in the 293 human embryonic kidney cell line that recapitulates AR biochemical activity as a steroid hormone receptor in prostate cancer cells. We used this system to identify putative AR-binding proteins in the cytosolic and nuclear compartments of mammalian cells using a large scale co-immunoprecipitation strategy coupled to quantitative mass spectrometry. For example, the heat shock 70 and 90 chaperones, which are known regulators of steroid hormone receptor, were identified as AR-binding proteins. AR purification enriched for proteins involved in RNA processing, protein transport, and cytoskeletal organization, suggesting a functional link between AR and these protein modules in mammalian cells. For example, AR purification in the nuclear compartment led to the specific enrichment of alpha-actinin-4, clathrin heavy chain, and serine-threonine protein kinase C delta. Short interfering RNA knockdown studies and co-transcriptional reporter assays revealed that clathrin heavy chain possessed co-activator activity during AR-mediated transcription, whereas alpha-actinin-4 and protein kinase C delta displayed both co-activator and co-repressor activity during AR-mediated transcription that was dependent upon their relative expression levels. Lastly immunohistochemical staining of prostate tissue showed that alpha-actinin-4 levels decreased in the nucleus of high grade cancerous prostate samples, suggesting its possible deregulation in advanced prostate cancers as previously observed in late stage metastatic breast cancers. Taken together, these findings suggest AR binds to specific protein modules in mammalian cells and that these protein modules may provide a molecular framework for interrogating AR function in normal and cancerous prostate epithelial cells.

Huntingtin-interacting protein 1-mediated neuronal cell death occurs through intrinsic apoptotic pathways and mitochondrial alterations

Huntingtin interacting protein-1 (Hip1) is known to be associated with the N-terminal domain of huntingtin. Although Hip1 can induce apoptosis, the exact upstream signal transduction pathways have not been clarified yet. In the present study, we examined whether activation of intrinsic and/or extrinsic apoptotic pathways occurs during Hip1-mediated neuronal cell death. Overexpression of Hip1 induced cell death through caspase-3 activation in immortalized hippocampal neuroprogenitor cells. Interestingly, proteolytic processing of Hip1 into partial fragments was observed in response to Hip1 transfection and apoptosis-inducing drugs. Moreover, Hip1 was found to directly bind to and activate caspase-9. This promoted cytosolic release of cytochrome c and apoptosis-inducing factor via mitochondrial membrane perturbation. Furthermore, Hip1 could directly bind to Apaf-1, suggesting that the neurotoxic signals of Hip1 transmit through the intrinsic mitochondrial apoptotic pathways and the formation of apoptosome complex.

The developing role of receptors and adaptors

The response of a cell to the myriad of signals that it receives is varied, and it is dependent on many different factors. The most-studied responses involve growth-factor signalling and these signalling cascades have become key targets for cancer therapy. Recent reports have indicated that growth-factor receptors and associated adaptors can accumulate in the nucleus. Are there novel functions for these proteins that might affect our understanding of their role in cancer and have implications for drug resistance?

Internet-based Profiler system as integrative framework to support translational research

Background

Translational research requires taking basic science observations and developing them into clinically useful tests and therapeutics. We have developed a process to develop molecular biomarkers for diagnosis and prognosis by integrating tissue microarray (TMA) technology and an internet-database tool, Profiler. TMA technology allows investigators to study hundreds of patient samples on a single glass slide resulting in the conservation of tissue and the reduction in inter-experimental variability. The Profiler system allows investigator to reliably track, store, and evaluate TMA experiments. Here within we describe the process that has evolved through an empirical basis over the past 5 years at two academic institutions.

Results

The generic design of this system makes it compatible with multiple organ system (e.g., prostate, breast, lung, renal, and hematopoietic system,). Studies and folders are restricted to authorized users as required. Over the past 5 years, investigators at 2 academic institutions have scanned 656 TMA experiments and collected 63,311 digital images of these tissue samples. 68 pathologists from 12 major user groups have accessed the system. Two groups directly link clinical data from over 500 patients for immediate access and the remaining groups choose to maintain clinical and pathology data on separate systems. Profiler currently has 170 K data points such as staining intensity, tumor grade, and nuclear size. Due to the relational database structure, analysis can be easily performed on single or multiple TMA experimental results. The TMA module of Profiler can maintain images acquired from multiple systems.

Conclusion

We have developed a robust process to develop molecular biomarkers using TMA technology and an internet-based database system to track all steps of this process. This system is extendable to other types of molecular data as separate modules and is freely available to academic institutions for licensing.

Huntingtin interacting protein 1 modulates the transcriptional activity of nuclear hormone receptors

Internalization of activated receptors regulates signaling, and endocytic adaptor proteins are well-characterized in clathrin-mediated uptake. One of these adaptor proteins, huntingtin interacting protein 1 (HIP1), induces cellular transformation and is overexpressed in some prostate cancers. We have discovered that HIP1 associates with the androgen receptor through a central coiled coil domain and is recruited to DNA response elements upon androgen stimulation. HIP1 is a novel androgen receptor regulator, significantly repressing transcription when knocked down using a silencing RNA approach and activating transcription when overexpressed. We have also identified a functional nuclear localization signal at the COOH terminus of HIP1, which contributes to the nuclear translocation of the protein. In conclusion, we have discovered that HIP1 is a nucleocytoplasmic protein capable of associating with membranes and DNA response elements and regulating transcription.

Serum Antibodies to Huntingtin Interacting Protein-1: A New Blood Test for Prostate Cancer

Huntingtin-interacting protein 1 (HIP1) is frequently overexpressed in prostate cancer. HIP1 is a clathrin-binding protein involved in growth factor receptor trafficking that transforms fibroblasts by prolonging the half-life of growth factor receptors. In addition to human cancers, HIP1 is also overexpressed in prostate tumors from the transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse model. Here we provide evidence that HIP1 plays an important role in mouse tumor development, as tumor formation in the TRAMP mice was impaired in the Hip1null/null background. In addition, we report that autoantibodies to HIP1 developed in the sera of TRAMP mice with prostate cancer as well as in the sera from human prostate cancer patients. This led to the development of an anti-HIP1 serum test in humans that had a similar sensitivity and specificity to the anti-alpha-methylacyl CoA racemase (AMACR) and prostate-specific antigen tests for prostate cancer and when combined with the anti-AMACR test yielded a specificity of 97%. These data suggest that HIP1 plays a functional role in tumorigenesis and that a positive HIP1 autoantibody test may be an important serum marker of prostate cancer.

Oncogenic breakdowns in endocytic adaptor proteins

Endocytosis is a versatile tool to regulate the intensity, localization, half-life and function of signaling complexes (signalosomes) that form in cells upon binding of growth factors, cytokines and morphogens to their cognate receptors. Endocytic adaptors are non-catalytic proteins that assemble effectors and structural components of the endocytic machinery around the trafficking cargo and serve as scaffolds for signalosomes, which in turn modify their location and activity by various post-translational modifications. We discuss how breakdowns in the function of endocytic adaptors might facilitate impairment of tissue homeostasis and consequent tumor development.

Poly(beta-amino ester)s promote cellular uptake of heparin and cancer cell death

Heparin/heparan sulfate-like glycosaminoglycans (HSGAGs) are involved in diverse cellular processes in the extracellular matrix (ECM). The biological effect of HSGAGs depends on disaccharide content and physiological location within the ECM. HSGAGs are also brought into cells during membrane transcytosis and growth factor signaling while protein bound. We sought to probe the impact of free HSGAGs within the cell by using heparin as a model HSGAG. A library of poly(beta-amino ester)s, which internalize DNA, was examined for the capacity of its members to internalize heparin. Fourteen polymers enabled heparin internalization. The most efficacious polymer reduced murine melanoma cell growth by 73%. No glycosaminoglycan was as efficacious as highly sulfated, full-length heparin. Internalized heparin likely interferes with transcription factor function and subsequently induces apoptotic cell death. Therefore, internalized heparin is a novel mechanism for inducing apoptosis of cancer cells.

HIP1: trafficking roles and regulation of tumorigenesis

During recent years, alterations in proteins of the endocytic pathway have been associated with tumors. Disrupted regulation of the endocytic pathway is a relatively unstudied mechanism of tumorigenesis, which can concomitantly disrupt several different signaling pathways to affect growth, differentiation and survival. Several endocytic proteins have been identified, either as part of tumor-associated translocations or to have the ability to transform cells. Here, we summarize the information known about huntingtin interacting protein 1 (HIP1), an endocytic protein with transforming properties that is involved in a cancer-causing translocation and which is overexpressed in a variety of human cancers. We describe the known normal functions of HIP1 in endocytosis and receptor trafficking, the evidence for its role as an oncoprotein and how HIP1 might be altered to promote tumorigenesis.

Hip1-related mutant mice grow and develop normally but have accelerated spinal abnormalities and dwarfism in the absence of HIP1

In mice and humans, there are two known members of the Huntingtin interacting protein 1 (HIP1) family, HIP1 and HIP1-related (HIP1r). Based on structural and functional data, these proteins participate in the clathrin trafficking network. The inactivation of Hip1 in mice leads to spinal, hematopoietic, and testicular defects. To investigate the biological function of HIP1r, we generated a Hip1r mutant allele in mice. Hip1r homozygous mutant mice are viable and fertile without obvious morphological abnormalities. In addition, embryonic fibroblasts derived from these mice do not have gross abnormalities in survival, proliferation, or clathrin trafficking pathways. Altogether, this demonstrates that HIP1r is not necessary for normal development of the embryo or for normal adulthood and suggests that HIP1 or other functionally related members of the clathrin trafficking network can compensate for HIP1r absence. To test the latter, we generated mice deficient in both HIP1 and HIP1r. These mice have accelerated development of abnormalities seen in Hip1 -deficient mice, including kypholordosis and growth defects. The severity of the Hip1r/Hip1 double-knockout phenotype compared to the Hip1 knockout indicates that HIP1r partially compensates for HIP1 function in the absence of HIP1 expression, providing strong evidence that HIP1 and HIP1r have overlapping roles in vivo.

Huntingtin Interacting Protein 1 mutations lead to abnormal hematopoiesis, spinal defects and cataracts

Huntingtin Interacting Protein 1 (HIP1) binds clathrin and AP2, is overexpressed in multiple human tumors, and transforms fibroblasts. The function of HIP1 is unknown although it is thought to play a fundamental role in clathrin trafficking. Gene-targeted Hip1-/- mice develop premature testicular degeneration and severe spinal deformities. Yet, although HIP1 is expressed in many tissues including the spleen and bone marrow and was part of a leukemogenic translocation, its role in hematopoiesis has not been examined. In this study we report that three different mutations of murine Hip1 lead to hematopoietic abnormalities reflected by diminished early progenitor frequencies and resistance to 5-FU-induced bone marrow toxicity. Two of the Hip1 mutant lines also display the previously described spinal defects. These observations indicate that, in addition to being required for the survival/proliferation of cancer cells and germline progenitors, HIP1 is also required for the survival/proliferation of diverse types of somatic cells, including hematopoietic progenitors.

HIP1 and HIP1r stabilize receptor tyrosine kinases and bind 3-phosphoinositides via epsin N-terminal homology domains

Huntingtin-interacting protein 1-related (HIP1r) is the only known mammalian relative of huntingtin-interacting protein 1 (HIP1), a protein that transforms fibroblasts via undefined mechanisms. Here we demonstrate that both HIP1r and HIP1 bind inositol lipids via their epsin N-terminal homology (ENTH) domains. In contrast to other ENTH domain-containing proteins, lipid binding is preferential to the 3-phosphate-containing inositol lipids, phosphatidylinositol 3,4-bisphosphate and phosphatidylinositol 3,5-bisphosphate. Furthermore, the HIP1r ENTH domain, like that of HIP1, is necessary for lipid binding, and expression of an ENTH domain-deletion mutant, HIP1r/deltaE, induces apoptosis. Consistent with the ability of HIP1r and HIP1 to affect cell survival, full-length HIP1 and HIP1r stabilize pools of growth factor receptors by prolonging their half-life following ligand-induced endocytosis. Although HIP1r and HIP1 display only a partially overlapping pattern of protein interactions, these data suggest that both proteins share a functional homology by binding 3-phosphorylated inositol lipids and stabilizing receptor tyrosine kinases in a fashion that may contribute to their ability to alter cell growth and survival.

Molecular markers to identify patients at risk for recurrence after primary treatment for prostate cancer

Accurate prognostication is a prerequisite for accurate therapeutics and management of prostate cancer because indolent tumors may require no intervention, whereas aggressive tumors lead to patient mortality. There is a critical need to define these subgroups of patients with prostate cancer differing in clinical outcome. Prognostic nomograms based on clinical data provide useful predictions of clinical states and outcomes, but they need further refinements to improve accuracy and universality. Genomic and proteomic analyses have provided many novel markers that may help define prognostic parameters based on the underlying biology of prostate cancer progression at the molecular level. These molecular markers are likely to augment traditional prognostic modalities by providing a set of molecularly defined and quantifiable variables. Encompassing the genome, transcriptome, and proteome of prostate cancer will likely provide "molecular signatures" that will bridge prognostication, prediction, and treatment in a single continuum.

Altered receptor trafficking in Huntingtin Interacting Protein 1-transformed cells

The clathrin-associated protein, Huntingtin Interacting Protein 1 (HIP1), is overexpressed in multiple human epithelial tumors. Here, we report that HIP1 is a novel oncoprotein that transforms cells. HIP1-transformed cells, in contrast to RasV12-transformed cells, have dysregulation of multiple receptors involved in clathrin trafficking. Examples include upregulation of the epidermal growth factor receptor (EGFR) and the transferrin receptor. Furthermore, accumulation of transferrin and EGF in the HIP1-transformed cells was increased, and breast tumors that had EGFR expressed also had HIP1 upregulated. Thus, HIP1 overexpression promotes tumor formation and is associated with a general alteration in receptor trafficking. HIP1 is the first endocytic protein to be directly implicated in tumor formation.

[Molecular diagnostics of prostate cancer]

Although a number of studies have identified molecular markers for prostate cancer, their clinical utility remains mainly unclear. Markers, which allow improved determination of the biological aggressiveness of individual prostate cancers, may help to optimize therapeutic management of this heterogeneous tumor type. Here, a subset of molecular markers, which are intensively discussed in the literature or which are supposed to gain clinical utility in the future, are described in more detail. For a better survey, the markers are divided into (a) susceptibility markers, (b) malignancy markers, and (c) aggressiveness markers. The number of markers described as well as the inconsistency across studies in assessing their clinical utility reflect the heterogeneity of prostate cancer also on a genetic level so that it is unlikely that a single marker will gain clinical relevance. Future research must include systematic analysis of the clinical utility of not only single markers but rather of marker profiles in appropriate studies.