Differences in Age at Onset of Symptoms, and Effects of Genetic Variants, in Patients With Early vs Late-Onset Idiopathic Chronic Pancreatitis in a North American Cohort.

BACKGROUND & AIMS: Idiopathic chronic pancreatitis (ICP) is the second most common subtype of CP. In 1994, researchers reported the bimodal age at onset of ICP symptoms: early onset ICP (EO-ICP; median age, 19.2 y) and late-onset ICP (LO-ICP; median age, 56.2 y). Ages of onset and clinical features of ICP differed from those of alcohol-related CP (ACP). However, variants in PRSS1 had not yet been associated with ICP. We reexamined ages of onset of ICP in a large, North American cohort of patients, and investigated the effects of genetic factors and alcohol use in patients with EO-ICP, LO-ICP, and ACP. METHODS: We performed a cross-sectional analysis of patients with CP of European ancestry enrolled in the North American Pancreatitis Study 2, a prospective study of 1195 patients with CP from 26 centers in the United States from August 2000 through December 2014. We compared age at onset of symptoms for 130 patients with CP who were lifetime abstainers from alcohol (61 patients with early onset and 69 patients with late onset), 308 light to moderate alcohol drinkers with CP, and 225 patients with ACP and heavy to very heavy alcohol use. DNA from available patients was analyzed for variants associated with CP in SPINK1, CFTR, and CTRC. The Kruskal-Wallis test was used to compare continuous variables across groups and based on genetic variants. RESULTS: Median ages at onset of symptoms were 20 years for patients with EO-ICP and no alcohol use, 58 years for patients with LO-ICP and no alcohol use, 47 years for light to moderate alcohol drinkers with CP, and 44 years for patients with ACP. A higher proportion of patients with EO-ICP had constant pain (65%) than patients with LO-ICP (31%) (P = .04). A higher proportion of patients with ACP had pseudocysts (43%) than patients with EO-ICP (11%) (P = .001). A higher proportion of patients with EO-ICP had pathogenic variants in SPINK1, CFTR, or CTRC (49%) than patients with LO-ICP (23%), light to moderate alcohol drinking with CP (26%), or ACP (23%) (P = .001). Among patients with variants in SPINK1, those with EO-ICP had onset of symptoms at a median age of 12 years, and light to moderate alcohol drinkers with CP had an age at onset of 24 years. Among patients with variants in CFTR, light to moderate alcohol drinkers had an age at onset of symptoms of 41 years, but this variant did not affect age at onset of EO-ICP or ACP. CONCLUSIONS: We confirmed previously reported ages at onset of symptoms for EO-ICP and LO-ICP in a North American cohort. We found differences in clinical features among patients with EO-ICP, LO-ICP, and ACP. Almost half of patients with EO-ICP have genetic variants associated with CP, compared with approximately one quarter of patients with LO-CP or ACP. Genetic variants affect ages at onset of symptoms in some groups.

Constant-severe pain in chronic pancreatitis is associated with genetic loci for major depression in the NAPS2 cohort.

BACKGROUND: Pain is the most debilitating symptom of recurrent acute pancreatitis (RAP) and chronic pancreatitis (CP) and often requires chronic opioids or total pancreatectomy with islet autotransplantation to manage. Pain is a complex experience that can be exacerbated by depression and vice versa. Our aim was to test the hypothesis that depression-associated genes are associated with a constant-severe pain experience in RAP/CP patients. STUDY: A retrospective study was done using North American Pancreatitis Study II (NAPS2) genotyped RAP and CP patients with completed case report forms (n = 1,357). Subjects were divided based on pattern of pain and pain severity as constant-severe pain (n = 787) versus not constant-severe pain (n = 570) to conduct a nested genome-wide association study. The association between reported antidepressant medication use and depression gene loci was tested. RESULTS: Constant-severe pain was reported in 58% (n = 787) of pancreatitis patients. No differences in sex or alcohol consumption were found based on pain severity. Antidepressant use was reported in 28% (n = 223), and they had lower SF-12 mental quality of life (MCS, p < 2.2 × 10- 16). Fifteen loci associated with constant-severe pain (p < 0.00001) were found to be in or near depression-associated genes including ROBO2, CTNND2, SGCZ, CNTN5 and BAIAP2. Three of these genes respond to antidepressant use (SGCZ, ROBO2, and CTNND2). CONCLUSION: Depression is a major co-factor in the pain experience. This genetic predisposition to depression may have utility in counseling patients and in instituting early antidepressant therapy for pain management of pancreatitis patients. Prospective randomized trials are warranted. CLINICAL TRIALS REGISTRATION: Clinicaltriasl.gov.# NCT01545167.

Complex Genetics in Pancreatitis: Insights Gained From a New Candidate Locus Panel.

OBJECTIVES: Chronic pancreatitis is the end stage of a pathologic inflammatory syndrome with multiple etiological factors, including genetic. We hypothesized that some pancreatitis etiology originates in pancreatic acinar or duct cells and requires both injury and compensatory mechanism failure. METHODS: One hundred pancreatitis patients were assessed using a DNA sequencing panel for pancreatitis. Cooccurrence of variants within and between genes was measured. Gene coexpression was confirmed via published single-cell RNA sequencing. RESULTS: One hundred and twenty-one variants were identified in 2 or more patients, 15 of which were enriched compared with reference populations. Single cell RNA-sequencing data verified coexpression of GGT1, CFTR, and PRSS1 in duct cells, PRSS1, CPA1, CEL, CTRC, and SPINK1 in acinar cells, and UBR1 in both. Multiple-risk variants with injury/stress effects (CEL, CFTR, CPA1, PRSS1) and impaired cell protection (CTRC, GGT1, SPINK1, UBR1) cooccur within duct cells, acinar cells, or both. CONCLUSIONS: Pancreatitis is a complex disorder with genetic interactions across genes and cell types. These findings suggest a new, non-Mendelian genetic risk/etiology paradigm where a combination of nonpathogenic genetic risk variants in groups of susceptibility genes and injury/dysfunction response genes contribute to acquired pancreatic disease.

Genetic Risk Score in Diabetes Associated With Chronic Pancreatitis Versus Type 2 Diabetes Mellitus.

INTRODUCTION: Diabetes mellitus (DM) is a complication of chronic pancreatitis (CP). Whether pancreatogenic diabetes associated with CP-DM represents a discrete pathophysiologic entity from type 2 DM (T2DM) remains uncertain. Addressing this question is needed for development of specific measures to manage CP-DM. We approached this question from a unique standpoint, hypothesizing that if CP-DM and T2DM are separate disorders, they should be genetically distinct. To test this hypothesis, we sought to determine whether a genetic risk score (GRS) based on validated single nucleotide polymorphisms for T2DM could distinguish between groups with CP-DM and T2DM. METHODS: We used 60 T2DM single nucleotide polymorphisms to construct a weighted GRS in 1,613 subjects from the North American Pancreatitis Study 2 and 2,685 subjects from the Multi-Ethnic Study of Atherosclerosis, all of European origin. RESULTS: The mean GRS was identical between 321 subjects with CP-DM and 423 subjects with T2DM (66.53 vs 66.42, P = 0.95), and the GRS of both diabetic groups was significantly higher than that of nondiabetic controls (n = 3,554, P < 0.0001). Exploratory analyses attempting to enrich the CP-DM group for pancreatogenic diabetes, such as eliminating diabetes diagnosed before CP, requiring pancreas-specific comorbidities, or removing those with a family history of diabetes, did not improve the ability of the GRS to distinguish between CP-DM and T2DM. DISCUSSION: Recognizing that we lacked a gold standard to define CP-DM, our study suggests that CP-DM may be a subtype of T2DM, a notion that should be tested in future, large prospective studies.

Known genetic susceptibility factors for chronic pancreatitis in patients of European ancestry are rare in patients of African ancestry.

BACKGROUND: Multiple pathogenic genetic variants are associated with pancreatitis in patients of European (EA) and Asian ancestries, but studies on patients of African ancestry (AA) are lacking. We evaluated the prevalence of known genetic variations in African-American subjects in the US. METHODS: We studied prospectively enrolled controls (n = 238) and patients with chronic (CP) (n = 232) or recurrent acute pancreatitis (RAP) (n = 45) in the NAPS2 studies from 2000-2014 of self-identified AA. Demographic and phenotypic information was obtained from structured questionnaires. Ancestry and admixture were evaluated by principal component analysis (PCA). Genotyping was performed for pathogenic genetic variants in PRSS1, SPINK1, CFTR and CTRC. Prevalence of disease-associated variants in NAPS2 subjects of AA and EA was compared. RESULTS: When compared with CP subjects of EA (n = 862), prevalence of established pathogenic genetic variants was infrequent in AA patients with CP, overall (29 vs. 8.19%, OR 4.60, 95% CI 2.74-7.74, p < 0.001), and after stratification by alcohol etiology (p < 0.001). On PCA, AA cases were more heterogeneous but distinct from EA subjects; no difference was observed between AA subjects with and without CP-associated variants. Of 19 A A patients with CP who had pathogenic genetic variants, 2 had variants in PRSS1 (R122H, R122C), 4 in SPINK1 (all N34S heterozygotes), 12 in CFTR (2 CFTRsev, 9 CFTRBD, 1 compound heterozygote with CFTRsev and CFTRBD), and 1 in CTRC (R254W). CONCLUSION: Pathogenic genetic variants reported in EA patients are significantly less common in AA patients. Further studies are needed to determine the complex risk factors for AA subjects with pancreatitis.

A sequence upstream of canonical PDZ-binding motif within CFTR COOH-terminus enhances NHERF1 interaction.

The development of cystic fibrosis transmembrane conductance regulator (CFTR) targeted therapy for cystic fibrosis has generated interest in maximizing membrane residence of mutant forms of CFTR by manipulating interactions with scaffold proteins, such as sodium/hydrogen exchange regulatory factor-1 (NHERF1). In this study, we explored whether COOH-terminal sequences in CFTR beyond the PDZ-binding motif influence its interaction with NHERF1. NHERF1 displayed minimal self-association in blot overlays (NHERF1, Kd = 1,382 ± 61.1 nM) at concentrations well above physiological levels, estimated at 240 nM from RNA-sequencing and 260 nM by liquid chromatography tandem mass spectrometry in sweat gland, a key site of CFTR function in vivo. However, NHERF1 oligomerized at considerably lower concentrations (10 nM) in the presence of the last 111 amino acids of CFTR (20 nM) in blot overlays and cross-linking assays and in coimmunoprecipitations using differently tagged versions of NHERF1. Deletion and alanine mutagenesis revealed that a six-amino acid sequence 1417EENKVR1422 and the terminal 1478TRL1480 (PDZ-binding motif) in the COOH-terminus were essential for the enhanced oligomerization of NHERF1. Full-length CFTR stably expressed in Madin-Darby canine kidney epithelial cells fostered NHERF1 oligomerization that was substantially reduced (∼5-fold) on alanine substitution of EEN, KVR, or EENKVR residues or deletion of the TRL motif. Confocal fluorescent microscopy revealed that the EENKVR and TRL sequences contribute to preferential localization of CFTR to the apical membrane. Together, these results indicate that COOH-terminal sequences mediate enhanced NHERF1 interaction and facilitate the localization of CFTR, a property that could be manipulated to stabilize mutant forms of CFTR at the apical surface to maximize the effect of CFTR-targeted therapeutics.

The Common Chymotrypsinogen C (CTRC) Variant G60G (C.180T) Increases Risk of Chronic Pancreatitis But Not Recurrent Acute Pancreatitis in a North American Population.

OBJECTIVES: Recurrent acute pancreatitis (RAP) is a complex inflammatory disorder that may progress to fibrosis and other irreversible features recognized as chronic pancreatitis (CP). Chymotrypsinogen C (CTRC) protects the pancreas by degrading prematurely activated trypsinogen. Rare mutations are associated with CP in Europe and Asia. We evaluated the occurrence of CTRC variants in subjects with RAP, CP, and controls from the North American Pancreatitis Study II cohort. METHODS: CP (n=694), RAP (n=448), and controls (n=1017) of European ancestry were evaluated. Subgroup analysis included CFTR and SPINK1 variants, alcohol, and smoking. RESULTS: We identified previously reported rare pathogenic CTRC A73T, R254W, and K247_R254del variants, intronic variants, and G60G (c.180 C>T; rs497078). Compared with controls (minor allele frequency (MAF)=10.8%), c.180T was associated with CP (MAF=16.8%, P<0.00001) but not RAP (MAF=11.9% P=NS). Trend test indicated co-dominant risk for CP (CT odds ratio (OR)=1.36, 95% confidence interval (CI)=1.13-1.64, P=0.0014; TT OR=3.98, 95% CI=2.10-7.56, P<0.0001). The T allele was significantly more frequent with concurrent pathogenic CFTR variants and/or SPINK1 N34S (combined 22.9% vs. 16.1%, OR 1.92, 95% C.I. 1.26-2.94, P=0.0023) and with alcoholic vs. non-alcoholic CP etiologies (20.8% vs. 12.4%, OR=1.9, 95% CI=1.30-2.79, P=0.0009). Alcohol and smoking generally occurred together, but the frequency of CTRC c.180 T in CP, but not RAP, was higher among never drinkers-ever smokers (22.2%) than ever drinker-never smokers (10.8%), suggesting that smoking rather than alcohol may be the driving factor in this association. CONCLUSIONS: The common CTRC variant c.180T acts as disease modifier that promotes progression from RAP to CP, especially in patients with CFTR or SPINK1 variants, alcohol, or smoking.

Mechanisms of CFTR functional variants that impair regulated bicarbonate permeation and increase risk for pancreatitis but not for cystic fibrosis.

CFTR is a dynamically regulated anion channel. Intracellular WNK1-SPAK activation causes CFTR to change permeability and conductance characteristics from a chloride-preferring to bicarbonate-preferring channel through unknown mechanisms. Two severe CFTR mutations (CFTRsev) cause complete loss of CFTR function and result in cystic fibrosis (CF), a severe genetic disorder affecting sweat glands, nasal sinuses, lungs, pancreas, liver, intestines, and male reproductive system. We hypothesize that those CFTR mutations that disrupt the WNK1-SPAK activation mechanisms cause a selective, bicarbonate defect in channel function (CFTRBD) affecting organs that utilize CFTR for bicarbonate secretion (e.g. the pancreas, nasal sinus, vas deferens) but do not cause typical CF. To understand the structural and functional requirements of the CFTR bicarbonate-preferring channel, we (a) screened 984 well-phenotyped pancreatitis cases for candidate CFTRBD mutations from among 81 previously described CFTR variants; (b) conducted electrophysiology studies on clones of variants found in pancreatitis but not CF; (c) computationally constructed a new, complete structural model of CFTR for molecular dynamics simulation of wild-type and mutant variants; and (d) tested the newly defined CFTRBD variants for disease in non-pancreas organs utilizing CFTR for bicarbonate secretion. Nine variants (CFTR R74Q, R75Q, R117H, R170H, L967S, L997F, D1152H, S1235R, and D1270N) not associated with typical CF were associated with pancreatitis (OR 1.5, p = 0.002). Clones expressed in HEK 293T cells had normal chloride but not bicarbonate permeability and conductance with WNK1-SPAK activation. Molecular dynamics simulations suggest physical restriction of the CFTR channel and altered dynamic channel regulation. Comparing pancreatitis patients and controls, CFTRBD increased risk for rhinosinusitis (OR 2.3, p<0.005) and male infertility (OR 395, p<<0.0001). WNK1-SPAK pathway-activated increases in CFTR bicarbonate permeability are altered by CFTRBD variants through multiple mechanisms. CFTRBD variants are associated with clinically significant disorders of the pancreas, sinuses, and male reproductive system.

Common genetic variants in the CLDN2 and PRSS1-PRSS2 loci alter risk for alcohol-related and sporadic pancreatitis.

Pancreatitis is a complex, progressively destructive inflammatory disorder. Alcohol was long thought to be the primary causative agent, but genetic contributions have been of interest since the discovery that rare PRSS1, CFTR and SPINK1 variants were associated with pancreatitis risk. We now report two associations at genome-wide significance identified and replicated at PRSS1-PRSS2 (P < 1 × 10(-12)) and X-linked CLDN2 (P < 1 × 10(-21)) through a two-stage genome-wide study (stage 1: 676 cases and 4,507 controls; stage 2: 910 cases and 4,170 controls). The PRSS1 variant likely affects disease susceptibility by altering expression of the primary trypsinogen gene. The CLDN2 risk allele is associated with atypical localization of claudin-2 in pancreatic acinar cells. The homozygous (or hemizygous in males) CLDN2 genotype confers the greatest risk, and its alleles interact with alcohol consumption to amplify risk. These results could partially explain the high frequency of alcohol-related pancreatitis in men (male hemizygote frequency is 0.26, whereas female homozygote frequency is 0.07).

Whole exome sequencing identifies multiple, complex etiologies in an idiopathic hereditary pancreatitis kindred.

CONTEXT: Hereditary pancreatitis is the early onset form of chronic pancreatitis that is carried in an autosomal dominant pattern with variable penetrance. While 80% of hereditary pancreatitis has been shown to be due to a single mutation in the trypsinogen gene PRSS1, a number of hereditary pancreatitis families have no identified genetic cause for illness; thus no reliable screening options or clear therapy. OBJECTIVE: To explore the use of massive parallel DNA sequencing technology to discover the etiology of pancreatitis in a family with idiopathic hereditary pancreatitis. DESIGN: Candidate gene screening and verification within a kindred. SETTING: Prospective cohort study, university based. PATIENTS OR PARTICIPANTS: Kindred with idiopathic hereditary pancreatitis. INTERVENTIONS: None. MAIN OUTCOME MEASURES: Identification of DNA variants predicted to increase susceptibility to pancreatitis. METHODS: Whole exome sequencing of two distantly related subjects with variant-specific confirmation in the subjects and other family members. RESULTS: We identified three deleterious genetic changes in the three major pancreatitis associated genes (PRSS1 CNV, SPINK1 c.27delC and CFTR R117H), two of which were carried by each patient. Individual targeted assays confirmed these variations in the two whole exome sequencing patients as well as affected and non-affected pedigree members. CONCLUSION: Whole exome sequencing was useful for rapid screening of candidate genes linked to pancreatitis. This method opens the door for time- and cost-effective screening of multiple disease-associated genes and modifying factors that associate in different ways to generate a complex genetic disorder.

TNF-alpha gene (TNFA) variants increase risk for multi-organ dysfunction syndrome (MODS) in acute pancreatitis.

BACKGROUND/OBJECTIVES: Acute pancreatitis (AP) is a complex inflammatory syndrome with unpredictable progression to systemic inflammation and multi-organ dysfunction syndrome (MODS). Tumor necrosis factor alpha (TNF-α) is a cytokine that may link inflammation to the systemic inflammatory response syndrome (SIRS), which usually precedes MODS. Small genetic cohort studies of the TNFA promoter in AP produced ambiguous results. We performed a comprehensive evaluation of TNFA promoter variants to assess both susceptibility to AP and risk of progression to MODS. METHODS: We prospectively ascertained 401 controls and 211 patients with AP that were assessed for persistent SIRS (>48 h) and MODS. MODS was defined as failure of ≥2 organ systems (cardiovascular, pulmonary, and/or renal) persisting more than 48 h. Subjects were genotyped by DNA sequencing and analyzed for SNPs at -1031 C/T (rs1799964), -863 A/C (rs1800630), -857 C/T (rs1799724), -308 A/G (rs1800629), and -238 A/G (rs361525). RESULTS: Twenty-three of 211 AP patients (11%) developed MODS. TNFA promoter variants were not associated with susceptibility to AP, but progression to MODS was associated with the minor allele at -1031C (56.5% vs. 32.4% P = 0.022, OR: 2.7; 95%CI: 1.12-6.51) and -863A (43.5% vs. 21.8% P = 0.022, OR: 2.76; 95%CI: 1.12-6.74). CONCLUSION: TNFA promoter variants do not alter susceptibility to AP, but rather the TNF-α expression-enhancing -1031C and -863A alleles significantly increased the risk of AP progression to MODS. These data, within the context of previous studies, clarify the risk of specific genetic variants in TNFA and therefore the role of TNF-α in the overall AP syndrome.

Genetics of pancreatitis.

PURPOSE OF REVIEW: Chronic pancreatitis is a syndrome characterized by chronic inflammation of the pancreas, with variable pain, calcifications, necrosis, fatty replacement, fibrosis and scarring and other complications. Disease susceptibility, severity, progression and pain patterns vary widely and do not necessarily parallel one another. Much of the variability in susceptibility to recurrent acute and chronic pancreatitis is now clearly shown to be related to genetic differences between patients. This review highlights recent advances and future directions in genetic research. RECENT FINDINGS: The strongest risk factors are associated with genetic variations in PRSS1, SPINK1, CFTR, and to a lesser extent, CTRC and CASR. The latest research suggest that a single factor rarely causes pancreatitis, and the majority of patients with recurrent acute and chronic pancreatitis have multiple variants in a gene, or epistatic interactions between multiple genes, coupled with environmental stressors. SUMMARY: Pancreatic diseases have a strong genetic component. Rather than a classic Mendelian disorder, recurrent acute and chronic pancreatitis represents truly complex diseases with the interaction and synergism of multiple genetic and environmental factors. The future will require new predictive models to guide prevention and therapy.

ABO blood group and chronic pancreatitis risk in the NAPS2 cohort.

OBJECTIVES: A risk association has been observed between non-O blood groups and pancreatic adenocarcinoma. Chronic pancreatitis also increases risk for pancreatic cancer, raising questions as to whether non-O blood groups are a risk for chronic pancreatitis and whether the pathophysiologic pathways are linked. Our goal was to determine whether ABO blood group may affect the risk of chronic pancreatitis. METHODS: The study cohort included chronic pancreatitis patients (n = 499) and healthy controls (n = 631) from the North American Pancreatitis Study 2 study. Genotyping was performed using Sequenom assay of rs8176746 A/C and rs505922 C/T to classify participants into ABO blood groups. RESULTS: O blood group was nonsignificantly more common among cases (44.7% vs 42.0%; P = 0.36), particularly among cases with alcohol-related chronic pancreatitis (49.3% vs 42%; P = 0.060). Alcoholic patients without coexisting high-risk PRSS1, CFTR, or SPINK1 variants had a significant overrepresentation of O blood type when compared with controls (odds ratio, 1.54; 95% confidence interval, 1.09-2.17; P = 0.01). CONCLUSIONS: A, B, and AB blood groups were not associated with a greater likelihood of having chronic pancreatitis and may decrease the risk of chronic pancreatitis in individuals who are very heavy drinkers. These results suggest that the mechanism linking non-O blood type with pancreatic pathology is specific to carcinogenesis.

Combined bicarbonate conductance-impairing variants in CFTR and SPINK1 variants are associated with chronic pancreatitis in patients without cystic fibrosis.

BACKGROUND & AIMS: Idiopathic chronic pancreatitis (ICP) is a complex inflammatory disorder associated with multiple genetic and environmental factors. In individuals without cystic fibrosis (CF), variants of CFTR that inhibit bicarbonate conductance but maintain chloride conductance might selectively impair secretion of pancreatic juice, leading to trypsin activation and pancreatitis. We investigated whether sequence variants in the gene encoding the pancreatic secretory trypsin inhibitor SPINK1 further increase the risk of pancreatitis in these patients. METHODS: We screened patients and controls for variants in SPINK1 associated with risk of chronic pancreatitis and in all 27 exons of CFTR. The final study group included 53 patients with sporadic ICP, 27 probands with familial ICP, 150 unrelated controls, 375 additional controls for limited genotyping. CFTR wild-type and p.R75Q were cloned and expressed in HEK293 cells, and relative conductances of HCO(3)(-) and Cl(-) were measured. RESULTS: SPINK1 variants were identified in 36% of subjects and 3% of controls (odds ratio [OR], 18.1). One variant of CFTR not associated with CF, p.R75Q, was found in 16% of subjects and 5.3% of controls (OR, 3.4). Coinheritance of CFTR p.R75Q and SPINK1 variants occurred in 8.75% of patients and 0.38% of controls (OR, 25.1). Patch-clamp recordings of cells that expressed CFTR p.R75Q showed normal chloride currents but significantly reduced bicarbonate currents (P = .0001). CONCLUSIONS: The CFTR variant p.R75Q causes a selective defect in bicarbonate conductance and increases risk of pancreatitis. Coinheritance of p.R75Q or CF causing CFTR variants with SPINK1 variants significantly increases the risk of ICP.

PDZ-binding motifs are unable to ensure correct polarized protein distribution in the absence of additional localization signals.

The C-terminal PDZ-binding motifs are required for polarized apical/basolateral localization of many membrane proteins. To determine the specificity of the PDZ-binding motifs in establishing cellular distribution, we utilized a 111-amino acid region from the C-terminus of cystic fibrosis transmembrane conductance regulator (CFTR) that is able to direct apical localization of fused reporter proteins. Substitution of the C-terminal PDZ-binding motif of CFTR with corresponding motifs necessary for basolateral localization of other membrane proteins did not lead to the redistribution of the fusion protein to the basolateral membrane. Instead, some fusion proteins remained localized to the apical membrane, whereas others showed no specific distribution. The specificity of the PDZ-based interactions was substantially increased when specific amino acids located upstream of the classical PDZ-binding motifs were included. However, even the presence of a longer C-terminal motif from a basolateral protein could not ensure basolateral distribution of the fusion protein. Our results indicate that the C-terminal PDZ-binding motifs are not the primary signals for polarized protein distribution, although they are required for targeting and/or stabilization of protein at the given location.

Regulation of colon carcinoma cell invasion by hypoxia-inducible factor 1.

Hypoxia-inducible factor 1 (HIF-1) transactivates genes the products of which mediate tumor angiogenesis and glycolytic metabolism. Overexpression of the HIF-1 alpha subunit, resulting from intratumoral hypoxia and genetic alterations, has been demonstrated in common human cancers and is correlated with tumor angiogenesis and patient mortality. Here we demonstrate that hypoxia or HIF-1 alpha overexpression stimulates Matrigel invasion by HCT116 human colon carcinoma cells, whereas this process is inhibited by a small interfering RNA directed against HIF-1 alpha. We show that HIF-1 regulates the expression of genes encoding cathepsin D; matrix metalloproteinase 2; urokinase plasminogen activator receptor (uPAR); fibronectin 1; keratins 14, 18, and 19; vimentin; transforming growth factor alpha; and autocrine motility factor, which are proteins that play established roles in the pathophysiology of invasion. Neutralizing antibodies against uPAR block tumor cell invasion induced by hypoxia or HIF-1 alpha overexpression. These results provide a molecular basis for promotion of the invasive cancer phenotype by hypoxia and/or HIF-1 alpha overexpression.