Heterogeneous nuclear ribonucleoprotein (hnRNP) binding to hormone response elements: A cause of vitamin D resistance

Abstract

In previous studies, we have shown that steroid hormone resistance in New World primates occurs in the absence of abnormal expression of cognate nuclear receptors. Rather, these animals have elevated levels of heterogeneous nuclear ribonucleoproteins (hnRNPs) that act as hormone response element-binding proteins and attenuate target gene transactivation. Here we present evidence for a similar mechanism in humans via a patient with resistance to the active form of vitamin D [1,25-dihydroxyvitamin D3 (1,25(OH)2D3)] who presented with normal vitamin D receptor (VDR) expression. Initial cotransfection studies showed that the cells of the patient suppressed basal and hormone-induced transactivation by wild-type VDR. Electrophoretic mobility-shift assays and Western͞Southwestern blot analyses indicated that this suppressive effect was due to overexpression of a nuclear protein that specifically interacts with a DNA response element known to bind retinoid X receptor-VDR heterodimers. Ab blocking in electrophoretic mobility-shift assays indicated that this dominant-negative acting protein was in the hnRNPA family of nucleic acid-binding proteins. Further studies have shown that several members of this family, most notably hnRNPA1, were able to suppress basal and 1,25(OH)2D3-induced luciferase activity. We therefore propose that this case of vitamin D resistance in a human subject is similar to that previously described for New World primates in which abnormal expression of a hormone response element-binding protein can cause target cell resistance to 1,25(OH)2D3. That this protein is a member of the hnRNP family capable of interacting with doublestranded DNA highlights a potentially important new component of the complex machinery required for steroid hormone signal transduction.A nalysis of inherited forms of steroid hormone resistance has greatly helped to clarify the underlying mechanisms by which molecules such as cortisol, testosterone, estradiol, and vitamin D achieve their actions (1, 2). In almost all cases, end organ resistance has been attributed to inactivating mutations of genes for intracellular steroid hormone receptors, despite the fact that a range of accessory proteins is required for steroid hormone signal transduction (3-5). However, recent reports have described novel forms of hormone resistance that have presented in the absence of a specific receptor gene mutation. These include an androgen receptor (AR)-positive patient with androgen insensitivity syndrome whose hormone resistance seems to be due to abnormal expression of a coactivator protein that interacts with the AF-1 domain of the AR (6). Accessory protein abnormality has also been proposed as the molecular defect in female siblings who presented with partial resistance to multiple steroid hormones (7). In view of these observations, it is possible to speculate that other forms of hormone resistance may also be due to abnormal accessory protein expression and function (8,9).We have shown that another class of proteins possibly acts as dominan...

Functional Impact of Heterogeneous Nuclear Ribonucleoprotein A2/B1 in Smooth Muscle Differentiation from Stem Cells and Embryonic Arteriogenesis

“…hnRNPA2/B1 is involved in various different nuclear activities, such as post-transcriptional regulation of RNA splicing and transportation or transcriptional regulation of c-Myc, apolipoprotein E (apo E), vitamin receptor gene, breast cancer 1 (BRCA1), and gonadotropin-releasing-hormone 1 (GnRH1) (22)(23)(24)(25)(26). Most hnRNPA2/B1 studies were carried out to study cancer cell metabolism and phenotype switch, which are related to alternative splicing (32-37).…”

“…For instance, studies showed that hnRNPA2/B1 regulates c-myc, apoE, vitamin D receptor, Brca1, and Gnrh1 gene expression by binding to related gene promoters (22)(23)(24)(25)(26). hnRNPA2/B1 has been reported as a gene transcriptional activator or repressor in different gene regulations.…”

“…However, accumulating evidence also suggests that RNA recognition motif and arginine/glycine-rich box of hnRNPs are involved in the binding of single-stranded DNA (17), telomere biogenesis (18,19), and transcriptional regulation (20,21). For example, it has been reported that hnRNPA2/B1 can bind to the promoters of c-myc, Apoe, vitamin D receptor, breast cancer 1, and gonadotropin-releasing hormone 1 genes and regulate the gene expressions (22)(23)(24)(25)(26). However, to date, there has been no report of the functional involvement of hnRNPA2/B1 in SMC differentiation and embryonic development.…”

Heterogeneous nuclear ribonucleoprotein A/B and G inhibits the transcription of gonadotropin-releasing-hormone 1

“…BLAST showed this unnamed puffer fish protein to be homologous to heterogeneous nuclear ribonucleoproteins A/B (hnRNP-A/B). Proteins in this hnRNP subfamily have been reported as transcriptional regulators in other species (Campillos et al, 2003;Chen et al, 2003;Gao et al, 2005Gao et al, , 2004a. The 37 kDa band matched best to hnRNP-A 0 (MS data not shown) with a lower protein score than the threshold score (68 vs. 78), indicating a possible false positive match due to sequence variance during evolution.…”

An Hsp27-related, Dominant-negative-acting Intracellular Estradiol-binding Protein

“…They squelch steroid hormonedirected transactivation by competing in trans with activated receptor proteins for the cognate hormone response elements of the receptor in the promoter of hormone-regulated genes. Expression and function of these proteins do not appear to be restricted to NWP, as we have described recently the first case of vitamin D-resistant rickets in a VDR-normal human subject who presented with constitutive overexpression of an hnRNPA1-like VDRE-BP (39). In the second class of epigenetic factors is the heat shock family of chaperone proteins (Hsp).…”