Dipeptidyl Peptidase IV Protein Research Articles

Design of some Apigenin derivatives as selective DPP-IV Inhibitors by Pharmacophore Modelling and its Validation through Molecular Dynamics Simulation

One of the most common forms of diabetes, type-2 diabetes mellitus is a chronic metabolic condition brought on by problems with insulin production or insulin resistance. By modifying blood glucose homeostasis, dipeptidyl peptidase-IV (DPP-IV) inhibition has the potential to treat type 2 diabetes. The quick development of computational drug design provided a fantastic opportunity to both discover and forecast the effectiveness of potential DPP-IV inhibitors. The current investigation supports and verifies the identification of new Apigenin derivatives as selective DPP-IV inhibitors. Schrodinger software was used to perform virtual screening (VS) of created compounds against DPP-IV, and the most promising hits were chosen. Out of 110 substances, 56 new apigenin derivatives were chosen for additional docking investigations using Glide based on their selectivity threshold followed by validation by pose selection method which is found to be below 2 Ǻ based on their superimposion with co-crystallized lgand. The DPP-IV protein was used as the target of molecular dynamic (MD) simulation studies to evaluate the correct binding mechanisms and stability of their complexes with enzyme. Structural chemistry was utilised to guide and considerably speed up the drug discovery process during the back-up development stages. It was also used to analyse in-silico suggestions and screening results, as well as to come up with fresh ideas. The study thus demonstrates the possibility of apigenin derivatives as highly specific DPP-IV inhibitors.

Quercetin and Coumarin Inhibit Dipeptidyl Peptidase-IV and Exhibits Antioxidant Properties: In Silico, In Vitro, Ex Vivo.

Quercetin and coumarin, two naturally occurring phytochemicals of plant origin, are known to regulate hyperglycemia and oxidative stress. The present study was designed to evaluate the inhibitory activity of quercetin and coumarin on dipeptidyl peptidase-IV (DPP-IV) and their antioxidant potential. DPP-IV inhibition assays were performed, and evaluated IC50 values of diprotin A, quercetin, coumarin, and sitagliptin were found to be 0.653, 4.02, 54.83, and 5.49 nmol/mL, respectively. Furthermore, in silico studies such as the drug-likeliness and docking efficiency of quercetin and coumarin to the DPP-IV protein were performed; the ex vivo antiperoxidative potential of quercetin and coumarin were also evaluated. The results of the present study showed that the DPP-IV inhibitory potential of quercetin was slightly higher than that of sitagliptin. Virtual docking revealed the tight binding of quercetin with DPP-IV protein. Quercetin and coumarin reduced oxidative stress in vitro and ex vivo systems. We report for the first time that both compounds inhibited the DPP-IV along with antioxidant activity and thus may be use as function food ingredients in the prevention of diabetes.

Enolase and dipeptidyl peptidase IV protein sub-unit vaccines are not protective against a lethal Streptococcus suis serotype 2 challenge in a mouse model of infection

BackgroundStreptococcus suis is a major swine pathogen causing arthritis, meningitis and sudden death in post-weaning piglets and is also a zoonotic agent. S. suis comprises 35 different serotypes of which the serotype 2 is the most prevalent in both pigs and humans. In the absence of commercial vaccines, bacterins (mostly autogenous), are used in the field, with controversial results. In the past years, the focus has turned towards the development of sub-unit vaccine candidates. However, published results are sometimes contradictory regarding the protective effect of a same candidate. Moreover, the adjuvant used may significantly influence the protective capacity of a given antigen. This study focused on two protective candidates, the dipeptidyl peptidase IV (DPPIV) and the enolase (SsEno). Both proteins are involved in S. suis pathogenesis, and while contradictory protection results have been obtained with SsEno in the past, no data on the protective capacity of DPPIV was available.ResultsResults showed that among all the field strains tested, 86 and 88% were positive for the expression of the SsEno and DPPIV proteins, respectively, suggesting that they are widely expressed by strains of different serotypes. However, no protection was obtained after two vaccine doses in a CD-1 mouse model of infection, regardless of the use of four different adjuvants. Even though no protection was obtained, significant amounts of antibodies were produced against both antigens, and this regardless of the adjuvant used.ConclusionsTaken together, these results demonstrate that S. suis DPPIV and SsEno are probably not good vaccine candidates, at least not in the conditions evaluated in this study. Further studies in the natural host (pig) should still be carried out. Moreover, this work highlights the importance of confirming results obtained by different research groups.

Hybrid docking-QSAR studies of DPP-IV inhibition activities of a series of aminomethyl-piperidones

In this study, the dipeptidyl peptidase-IV (DPP-IV) inhibition activities of a series of novel aminomethyl-piperidones were investigated by molecular docking studies and modeled by quantitative structure–activity relationship (QSAR) methodology. Molecular docking studies were used to find the best conformations of the studied molecules in the active site of DPP-IV protein. Then the best docking-derived conformation for each molecule was applied for calculating the molecular descriptors. Multiple linear regression (MLR) and Levenberg–Marquardt artificial neural network (LM-ANN) were conducted on descriptors derived by docking. The results of these models revealed the superiority of LM-ANN model over MLR which showed the nonlinear relationship between the selected molecular descriptors and DPP-IV inhibition activities of studied molecules. The correlation coefficient (R) and standard error (SE) of ANN model were 0.983 and 0.103 for the training set and 0.966 and 0.168 for the external test set. These results showed a close agreement between the experimental and calculated values of pIC50 which demonstrated the robustness of LM-ANN model in modeling of aminomethyl-piperidones. Applicability domain analysis and sensitivity analysis were applied on the obtained models. This study gives useful information for further experimental studies on DPP-IV inhibitors. The results of this work reveal the applicability of hybrid docking-QSAR methodology in ligand-protein studies.

Regulation of Dipeptidyl Peptidase IV in the Post-stroke Rat Brain and In Vitro Ischemia: Implications for Chemokine-Mediated Neural Progenitor Cell Migration and Angiogenesis.

Cerebral ischemia evokes abnormal release of proteases in the brain microenvironment that spatiotemporally impact angio-neurogenesis. Dipeptidyl peptidase IV (DPPIV), a cell surface and secreted protease, has been implicated in extracellular matrix remodeling by regulating cell adhesion, migration, and angiogenesis through modifying the functions of the major chemokine stromal-derived factor, SDF1. To elucidate the possible association of DPPIV in ischemic brain, we examined the expression of DPPIV in the post-stroke rat brain and under in vitro ischemia by oxygen glucose deprivation (OGD). We further investigated the effects of DPPIV on SDF1 mediated in vitro chemotactic and angiogenic functions. DPPIV protein and mRNA levels were significantly upregulated during repair phase in the ischemic cortex of the rat brain, specifically in neurons, astrocytes, and endothelial cells. In vitro exposure of Neuro-2a neuronal cells and rat brain endothelial cells to OGD resulted in upregulation of DPPIV. In vitro functional analysis showed that DPPIV decreases the SDF1-mediated angiogenic potential of rat brain endothelial cells and inhibits the migration of Neuro-2a and neural progenitor cells. Western blot analyses revealed decreased levels of phosphorylated ERK1/2 and AKT in the presence of DPPIV. DPPIV inhibitor restored the effects of SDF1. Proteome profile array screening further revealed that DPPIV decreases matrix metalloproteinase-9, a key downstream effector of ERK-AKT signaling pathways. Overall, delayed induction of DPPIV in response to ischemia/reperfusion suggests that DPPIV may play an important role in endogenous brain tissue remodeling and repair processes. This may be mediated through modulation of SDF1-mediated cell migration and angiogenesis.

Obese patients have higher circulating protein levels of dipeptidyl peptidase IV

Dipeptidyl peptidase IV (DPPIV) is a protease with broad distribution involved in various homeostatic processes such as immune defense, psychoneuroendocrine functions and nutrition. While DPPIV protein levels were investigated in patients with hyporectic disorders, less is known under conditions of obesity. Therefore, we investigated DPPIV across a broad range of body mass index (BMI). Blood samples from hospitalized patients with normal weight (BMI 18.5–25kg/m2), anorexia nervosa (BMI <17.5kg/m2) and obesity (BMI 30–40, 40–50 and >50kg/m2, n=15/group) were tested cross-sectionally and DPPIV concentration and total enzyme activity and the DPPIV targets, pancreatic polypeptide (PP) and glucagon-like peptide (GLP-1) were measured. DPPIV protein expression was detected in human plasma indicated by a strong band at the expected size of 110kDa and another major band at 50kDa, likely representing a fragment comprised of two heavy chains. Obese patients had higher DPPIV protein levels compared to normal weight and anorexics (+50%, p<0.05) resulting in a positive correlation with BMI (r=0.34, p=0.004). DPPIV serum activity was similar in all groups (p>0.05), while the concentration/activity ratio was higher in obese patients (p<0.05). Plasma PP levels were highest in anorexic patients (∼2-fold increase compared to other groups, p<0.05), whereas GLP-1 did not differ among groups (p<0.05). Taken together, circulating DPPIV protein levels depend on body weight with increased levels in obese resulting in an increased concentration/activity ratio. Since DPPIV deactivates food intake-inhibitory hormones like PP, an increased DPPIV concentration/activity ratio might contribute to reduced food intake-inhibitory signaling under conditions of obesity.

Novel hydrazine derivatives as selective DPP-IV inhibitors: findings from virtual screening and validation through molecular dynamics simulations

The present study demonstrates and validates the discovery of two novel hydrazine derivatives as selective dipeptidyl peptidase-IV (DPP-IV) inhibitors. Virtual screening (VS) of publicly available databases was performed using virtual screening workflow (VSW) of Schrödinger software against DPP-IV and the most promising hits were selected. Selectivity was further assessed by docking the hits against homology modeled structures of DPP8 and DPP9. Two novel hydrazine derivatives were selected for further studies based on their selectivity threshold. To assess their correct binding modes and stability of their complexes with enzyme, molecular dynamic (MD) simulation studies were performed against the DPP-IV protein and the results revealed that they had a better binding affinity towards DPP-IV as compared to DPP 8 and DPP 9. The binding poses were further validated by docking these ligands with different softwares (Glide and Gold). The proposed binding modes of hydrazines were found to be similar to sitagliptine and alogliptine. Thus, the study reveals the potential of hydrazine derivatives as highly selective DPP-IV inhibitors.

Identification of altered dipeptidyl-peptidase activities as potential biomarkers for unipolar depression

BackgroundChanges in circulatory aminopeptidases [dipeptidyl-peptidase-IV (DPP-IV), Prolyl-oligopeptidase (POP) and Leucine aminopeptidase (LAP)] activities have been found to be associated with psychiatric illnesses and inflammatory diseases. MethodsThe discriminatory indices of aminopeptidases activities were assessed by enzymatic assays in plasma samples from 240 unipolar depression (UD) patients and 264 matched controls. In addition the relationship between soluble and cellular DPP-IV activity was determined in plasma and blood cells from healthy subjects. ResultsGreater than 95% of the plasma DPP-IV activity could be blocked by inhibitors, demonstrating the specificity of the assay. Also, DPP-IV protein and activity levels were strongly correlated. In contrast, only 50% of the membrane-bound activity in blood cells was inhibited, which suggested that other similar peptidases may be present in these cells. UD patients had decreased plasma levels of DPP-IV and POP activities compared to healthy controls with a concomitant increase in LAP activity. Finally, testing of the LAP/DPP-IV ratio resulted in good discrimination of UD patients from controls with an area under the curve—receiver operating characteristic of 0.70. LimitationsFurther biological validation studies using different cohorts are warranted. ConclusionsThe finding that plasma DPP-IV activity was decreased and LAP activity was increased in UD patients suggests the potential value for testing the levels of these enzymes for improved classification of patients. In addition, the changes in these enzymes, suggests that the proteolytic maturation of their proneuropeptide and prohormone subtrates may also be affected in UD, resulting in altered production of the associated bioactive peptides.

Aqueous seed extract of Syzygium cumini inhibits the dipeptidyl peptidase IV and adenosine deaminase activities, but it does not change the CD26 expression in lymphocytes in vitro

Syzygium cumini (Sc) have been intensively studied in the last years due its beneficial effects including anti-diabetic and anti-inflammatory potential. Thus, the aim of this study was to evaluate the effect of aqueous seed extract of Sc (ASc) in the activity of enzymes involved in lymphocyte functions. To perform this study, we isolated lymphocytes from healthy donors. Lymphocytes were exposed to 10, 30, and 100mg/mL of ASc during 4 and 6h and adenosine deaminase (ADA), dipeptidyl peptidase IV (DPP-IV), and acetylcholinesterase (AChE) activities as well as CD26 expression and cellular viability were evaluated. ASc inhibited the ADA and DPP-IV activities without alteration in the CD26 expression (DPP-IV protein). No alterations were observed in the AChE activity or in the cell viability. These results indicate that the inhibition of the DPP-IV and ADA activities was dependent on the time of exposition to ASc. We suggest that ASc exhibits immunomodulatory properties probably via the pathway of DPP-IV-ADA complex, contributing to the understanding of these proceedings in the purinergic signaling.

Neuropeptide Y overflow and metabolism in skeletal muscle arterioles

The purpose of this study was to characterize neuropeptide Y (NPY) overflow and metabolism from isolated skeletal muscle arterioles of female rats. Gastrocnemius first-order arterioles were removed from young (2 months), young adult (6 months) and middle-aged (12 months) F344 female rats. Arterioles were isolated, cannulated and pressurized in a microvessel bath with field stimulation electrodes. NPY overflow from isolated arterioles was assessed at 0 s and 30 s post-field stimulation. Dipeptidyl peptidase IV (DPPIV) activity was quantified via fluorometric assay of whole vessel homogenate. In young adult and middle-aged rats, NPY overflow increased 0 s and 30 s following field stimulation. In young adult rats, DPPIV inhibition resulted in an increase in NPY overflow at 30 s, while middle-aged rats had no increase in NPY overflow with DPPIV inhibition (P <0.05). DPPIV activity was influenced by factors such as age, vessel type, and endothelium (P <0.05). The present data suggest that DPPIV plays a significant role in modulating the actions of NPY in arterioles of young adult females; however, this role appears to diminish with age.

Dipeptidyl peptidase IV (DPPIV), a candidate tumor suppressor gene in melanomas is silenced by promoter methylation

Dipeptidyl peptidase IV (DPPIV), a serine protease is expressed by normal melanocytes but not by melanomas, the malignant counterpart. DPPIV is encoded by a gene that contains a 5 CpG island spanning a transcriptional regulatory region. Previously we have demonstrated that DPPIV abrogates growth factor independence and functions as a tumor suppressor gene in melanomas. In this study we show that loss of DPPIV occurs at RNA level and demethylating agent, 5-aza-2'-deoxycytidine (5-AZA-Cdr) treatment of DPPIV negative melanoma cell lines results in increase of DPPIV mRNA, protein, and enzyme activities. By using sodium bisulfite genomic DNA modifications, PCR, and sequencing we confirmed that DPPIV gene promoter is methylated in eight out of ten melanoma cell lines tested. Further more, 5-AZA-Cdr induced increases in DPPIV levels correlated with growth inhibition and apoptosis in melanoma cells. All together these findings suggest that frequent downregulation of DPPIV expression in melanoma can be attributed, in large part, to aberrant promoter hypermethylation and this loss of DPPIV may be a critical event contributing to melanoma development.

Adenosine Down-Regulates the Surface Expression of Dipeptidyl Peptidase IV on HT-29 Human Colorectal Carcinoma Cells: Implications for Cancer Cell Behavior

Dipeptidyl peptidase IV (DPPIV) is a multifunctional cell-surface protein that, as well as having dipeptidase activity, is the major binding protein for adenosine deaminase (ADA) and also binds extracellular matrix proteins such as fibronectin and collagen. It typically reduces the activity of chemokines and other peptide mediators as a result of its enzymatic activity. DPPIV is aberrantly expressed in many cancers, and decreased expression has been linked to increases in invasion and metastasis. We asked whether adenosine, a purine nucleoside that is present at increased levels in the hypoxic tumor microenvironment, might affect the expression of DPPIV at the cell surface. Treatment with a single dose of adenosine produced an initial transient (1 to 4 hours) modest (approximately 10%) increase in DPPIV, followed by a more profound (approximately 40%) depression of DPPIV protein expression at the surface of HT-29 human colon carcinoma cells, with a maximal decline being reached after 48 hours, and persisting for at least a week with daily exposure to adenosine. This down-regulation ofDPPIV occurred at adenosine concentrations comparable to those present within the extracellular fluid of colorectal tumors growing in vivo, and was not elicited by inosine or guanosine. Neither cellular uptake of adenosine nor its phosphorylation was necessary for the down-regulation of DPPIV. The decrease in DPPIV protein at the cell surface was paralleled by decreases in DPPIV enzyme activity, binding of ADA, and the ability of the cells to bind to and migrate on cellular fibronectin. Adenosine, at concentrations that exist within solid tumors, therefore acts at the surface of colorectal carcinoma cells to decrease levels and activities of DPPIV. This down-regulation of DPPIV may increase the sensitivity of cancer cells to the tumor-promoting effects of adenosine and their response to chemokines and the extracellular matrix, facilitating their expansion and metastasis.

Involvement of Dipeptidyl Peptidase IV in Immune Complex–Mediated Glomerulonephritis

Dipeptidyl peptidase IV (DPPIV) is widely expressed in many tissues; however, its precise biological function is poorly understood. One of its possible physiologic roles is an involvement in the immune system, which plays a pivotal role in the pathogenesis of glomerulonephritis. The present study focused on the involvement of DPPIV in immune complex–mediated glomerulonephritis. Experimental nephritis was induced by anti-Thy-1.1 monoclonal antibody E30 using Wistar or F344 rats. The application of a new monoclonal antibody against DPPIV, F16, completely suppressed E30-induced proteinuria and mesangial proliferation in Wistar rats, whereas these preventive effects of F16 were not observed in F344 rats, which spontaneously lack DPPIV protein. Treatment with F16 inhibited glomerular deposition of complement C3 and complement C4 after the binding of E30 to the mesangial cell surface. Because the preventive effect of F16 was attributable to suppression of the complement cascade, we examined its influences on complement-dependent mesangial cell lysis in vitro. We discovered that the complement cascade was markedly inactivated in F16-treated Wistar rat serum but not in F16-treated F344 rats. These results indicate that DPPIV may play a somewhat crucial role in regulating the complement cascade and that inhibition of DPPIV may serve as a new target for preventing complement-dependent tissue injury.

Dipeptidyl peptidase IV (DPPIV) inhibits cellular invasion of melanoma cells.

Dipeptidyl peptidase IV (DPPIV) is a 110-kD, trans-membrane, ectoenzyme, with ubiquitous expression. DPPIV has numerous functions including involvement in T-cell activation, cell adhesion, digestion of proline containing peptides in the kidney and intestines, HIV infection and apoptosis, and regulation of tumorigenicity in certain melanoma cells. Constitutively expressed on numerous epithelial cell types, DPPIV is often disregulated in a variety of human malignancies. The most striking evidence of DPPIV down-regulation is found in transformed melanocytes. where nearly 100% of melanomas lack DPPIV expression. We have identified DPPIV as a gene that can alter the invasive potential of a number of melanoma cell lines. By transfecting the full-length cDNA of DPPIV, we have established stable melanoma cell lines that express comparable levels of the DPPIV protein as normal epidermal melanocytes. Matrigel invasion assays were utilized to study the effects of DPPIV expression on the invasive potential of these cells. The parental and vector transfectants readily migrated across the Matrigel while the invasiveness of DPPIV transfected cells was reduced by greater than 75%. The effects on cellular invasion are not attributed to overall growth characteristics, as both DPPIV expressing and non-expressing cells behave comparably in culture. We have also constructed mutants of DPPIV that lack either the extra-cellular serine protease activity or the six amino acid cytoplasmic domain. Both mutants were stably expressed in melanoma cells. Matrigel invasion assays performed with cells expressing the two mutant forms of the protein revealed phenotypic effects similar to wild type function. In this study. we have demonstrated that expression of a proteolytically active form of the DPPIV protein inhibits the invasiveness of malignant melanoma cell lines lacking endogenous DPPIV expression. Furthermore, we have shown that neither the protease activity nor the cytoplasmic domain of DPPIV is required for its anti-invasive activity.

CD26/dipeptidyl peptidase IV expression in human lymphomas is restricted to CD30-positive anaplastic large cell and a subset of T-cell non-Hodgkin's lymphomas

CD26 is identical to the cell surface ectoenzyme dipeptidyl peptidase IV (DPPIV). CD26 DPPIV is associated with T-cell activation and proliferation and also may function as an auxiliary adhesion factor. Although CD26 DPPIV has been previously studied on lymphoid populations and on leukemias/lymphomas of B- and T-cell phenotype, little is known about its expression and functional role in some specific types of lymphomas, such as CD30-positive anaplastic large cell (ALC) lymphomas and Hodgkin's disease (HD). A series of 81 lymphoma samples, including 23 cases of HD, 17 cases of CD30-positive ALC lymphomas, 41 cases of other non-Hodgkin's lymphomas (NHL), and a panel of HD- or ALC lymphoma-derived human cell lines were evaluated for CD26 DPPIV expression by enzyme histochemistry and immunohistochemistry on frozen sections and cell smears. CD26 DPPIV protein was expressed on neoplastic cells in 12 of 17 (71%) ALC lymphomas irrespective of their antigenic phenotype and in seven of 15 (47%) T-cell NHLs. In contrast, we did not detect CD26 DPPIV expression in tumor cells from 26 cases of B-cell NHL other than ALC lymphomas or in Reed Sternberg (RS) cells and variants of 21 of 23 HD cases. Accordingly, CD26 DPPIV expression was maintained on the CD30-positive ALC lymphoma cell line Karpas 299, but the molecule was not detected on HD-derived cell lines of B, T, or non-B non-T phenotype. These results may support a new potential tool for the phenotypic separation of ALC lymphomas from HD based on the differential expression of the CD26 DPPIV molecule. Moreover, given the demonstration that CD26 DPPIV is identical to the human adenosine deaminase (ADA) binding protein, it could be speculated that CD26 DPPIV also may function by interacting with ADA to regulate the growth of CD26 DPPIV expressing neoplastic cells in ALC lymphomas.

Apical cell surface expression of rat dipeptidyl peptidase IV in transfected Madin-Darby canine kidney cells

Dipeptidyl peptidase IV (DPPIV) is a type II membrane glycoprotein that is predominantly localized to the apical plasma membrane in various epithelial cells. In order to understand in more detail the biogenesis and sorting of DPPIV, the cDNA for rat DPPIV was inserted into a mammalian plasmid expression vector so that DPPIV expression was driven by a control region composed of the SV40 early promoter region fused to the enhancer of the Rous sarcoma virus. Madin-Darby canine kidney cells transfected with this construct were found to express the DPPIV protein. In these transfected cells, the majority of DPPIV was present on the apial cell surface. This observation suggests that the information for apical surface localization is inherent in the DPPIV molecule itself and that this sorting information is decipherable in the epithelial cells of a different species. DPPIV is transported efficiently from the endoplasmic reticulum to the Golgi apparatus as assessed by pulse-chase experiments. Furthermore, evidence is presented which suggests that the majority of DPPIV is sorted intracellularly to the apical cell surface. The same protein has, however, been reported to be sorted by an indirect pathway through transcytosis from the basolateral to the apical cell surface in hepatocytes (Bartles, J.R., Feracci, H., M., Stinger, B., and Hubbard, A.L. (1987) J. Cell Biol. 105, 1241-1251). This study suggests that the same protein can take two different pathways in different cell types for its correct apical cell surface localization.

Expression of dipeptidyl peptidase IV in rat tissues is mainly regulated at the mRNA levels

Dipeptidyl peptidase IV (DPPIV) is a serine peptidase that cleaves N-terminal dipeptides from polypeptides when the second residue is a proline or an alanine. We have recently cloned cDNAs for rat gp110, a membrane glycoprotein with Mr of 110,000 isolated initially from rat liver. Studies reported here establish that the gp110 for which we have cloned cDNAs is DPPIV. Using the antibodies against and cDNA for DPPIV, we have assessed the tissue distribution of DPPIV by molecular approaches. Immunoblot analysis demonstrated that DPPIV is present in the kidney, lung, and small intestine at high levels, in the liver and spleen at moderate levels, and in the heart at low levels. The highest levels of mRNA for DPPIV were detected in the kidney and small intestine as compared to moderate levels found in the lung, liver, and spleen. The lowest levels of DPPIV mRNA were found in the stomach, testis, and heart. No detectable DPPIV protein and mRNA were found in brain or muscle. LDPPIV protein and mRNA are present at much lower levels in fetal livers as compared to the adult liver. Indirect immunofluorescence microscopy demonstrated that DPPIV is localized in the bile canaliculus of hematocytes and in the apical membrane domains of kidney tubule and small intestine. Further studies by Southern blot analysis indicate that DPPIV is encoded by a single gene.