Carbonic anhydrases III and IX are new players in the crosstalk between adrenocortical carcinoma and its altered adipose microenvironment

PURPOSE

Adrenocortical carcinoma (ACC), a rare malignancy of the adrenocortex, is characterized by a crosstalk between the adipose microenvironment and tumor. Here, we assessed the involvement of carbonic anhydrase (CA) enzymes III and IX (CAIII and CAIX), in the metabolic alterations of the adipose tissue characterizing obesity and in the local crosstalk between the tumor adipose microenvironment and ACC.

RESULTS/METHODS

CAIII and CAIX expression is altered in visceral adipose tissue (VAT) in obesity and in ACC. A significant CAIX upregulation was present in ACC at advanced stages (n = 14) (fold increase FI = 7.4 ± 0.1, P < 0.05) associated with lower CAIII levels (FI = 0.25 ± 0.06, P < 0.001), compared with lower stages (n = 9). In vitro coculture between visceral adipose stem cells (ASCs) and ACC cell lines, H295R and MUC-1, mimicking the interaction occurring between VAT and advanced ACC, showed a significant CAIX upregulation in H295R but not in MUC-1 cells, and a decreased expression of CAIII. The effect on adipose cells was different when cocultured with H295R or MUC-1 cells. Coculture did not modulate CAIII expression in ASCs, which, however, was significantly downregulated with H295R (FI = 0.34 ± 0.11, P < 0.05) and upregulated by MUC-1 when cocultured ASCs were induced to differentiate toward adipocytes, with an expression profile similar to what found in VAT of obese subjects. CAIX expression was markedly increased in ASCs cocultured with H295R and to a less extent following adipogenesis induction (FI = 150.9 ± 46.5 and FI = 4.6 ± 1.1, P < 0.01, respectively).

CONCLUSION

Our findings highlight a modulation of CAIII and CAIX in the metabolic crosstalk between ACC and its local adipose microenvironment, suggesting that CAs might represent a potential target for novel anticancer therapies.

Management and outcome of metastatic pheochromocytomas/paragangliomas: a monocentric experience

BACKGROUND

Pheochromocytoma (PHEO) and paraganglioma (PGL) are rare neuroendocrine tumors releasing catecholamines. Metastatic pheochromocytomas/paragangliomas (PPGLs) occur in about 5-26% of cases. To date, the management of patients affected by metastatic disease is a challenge in the absence of guidelines.

AIM

The aim of this study was to evaluate the overall survival (OS) and the progression-free survival (PFS) in metastatic PPGLs.

METHODS

Clinical data of 20 patients referred to the Careggi University Hospital (Florence, Italy) were retrospectively collected. Follow-up ranged from 1989 to 2019. Site and size of primary tumor, biochemical activity, genetic analysis and employed therapies were considered. Data were analyzed with SPSS version 27.

RESULTS

Nine PHEOs (45%) and 11 PGLs (55%) were enrolled. Median age at diagnosis was 43.5 years [30-55]. Mean follow-up was 104.6 ± 89.3 months. Catecholamines were released in 70% of cases. An inherited disease was reported in 50% of patients. OS from the initial diagnosis (OSpt) and from the metastatic appearance (OSmtx) were lower in older patients (OSpt p = 0.028; OSmtx p < 0.001), abdominal PGLs (OSpt p = 0.007; OSmtx p = 0.041), larger tumors (OSpt p = 0.008; OSmtx p = 0.025) and sporadic disease (OSpt p = 0.013; OSmtx p = 0.008).

CONCLUSION

Our data showed that older age at the initial diagnosis, sympathetic extra-adrenal localization, larger tumors and wild-type neoplasms are related to worse prognosis. Notably, the employed therapies do not seem to influence the survival of our patients. At present, effective treatments for metastatic PPGLs are missing and a multidisciplinary approach is indispensably required.

Adrenocortical carcinoma: the dawn of a new era of genomic and molecular biology analysis

Over the last decade, the development of novel and high penetrance genomic approaches to analyze biological samples has provided very new insights in the comprehension of the molecular biology and genetics of tumors. The use of these techniques, consisting of exome sequencing, transcriptome, miRNome, chromosome alteration, genome, and epigenome analysis, has also been successfully applied to adrenocortical carcinoma (ACC). In fact, the analysis of large cohorts of patients allowed the stratification of ACC with different patterns of molecular alterations, associated with different outcomes, thus providing a novel molecular classification of the malignancy to be associated with the classical pathological analysis. Improving our knowledge about ACC molecular features will result not only in a better diagnostic and prognostic accuracy, but also in the identification of more specific therapeutic targets for the development of more effective pharmacological anti-cancer approaches. In particular, the specific molecular alteration profiles identified in ACC may represent targetable events by the use of already developed or newly designed drugs enabling a better and more efficacious management of the ACC patient in the context of new frontiers of personalized precision medicine.

Clinical relevance of phenotype/genotype correlations in the diagnosis and therapy of pheochromocytomas/paragangliomas

Pheochromocytomas and paragangliomas are tumors arising from neural crest-derived cells. They can be sympathetic in origin, catecholamine secreting and located in the abdomen or chest, or parasympathetic, generally non-secreting and located in the head and neck region. It is well established that about 35% of them are genetically determined. Germ-line mutations in one of the 10 so far known susceptibility genes is especially suspected when the tumors are diagnosed in young patients, multiple or recurrent or associated with additional lesions typical of syndromic clinical pictures such as von Hippel-Lindau, Multiple Endocrine Neoplasia type 2 or Neurofibromatosis type 1. Tumor genetic profile determines the type and pattern of catecholamine release, the clinical presentation, the risk of malignancy and may influence the choice of the radiotracers used in functional imaging, the type of surgical procedures as well as the type of medical therapy in the treatment of metastatic disease.

Mitochondrial function and content in pheochromocytoma/paraganglioma of succinate dehydrogenase mutation carriers

To date, the consequences of succinate dehydrogenase (SDH) impairment on overall mitochondrial functions are still obscure. In this study, we evaluated SDH activity and expression and mitochondrial homeostasis in 57 tissue samples of pheochromocytoma (PHEO)/paraganglioma (PGL) obtained from patients genotyped for PHEO/PGL susceptibility genes. The resulted SDH activity and content always decreased in SDH-mutated tumors, in one out of two MAX-mutated patients and in four patients resulted wild type (wt) at genetic screening. All these four wt patients were further screened for large deletions in SDH genes, TMEM127 and MAX and resulted wt but two had somatic SDHD mutations. The RT-PCR in the MAX-mutated sample suggests that the decrease in SDH depends on complex instability and not on a reduced SDHB expression. SDH mutations neither alter citrate synthase (CS) activity nor the content of voltage-dependent anion channel (VDAC) while the expression of the mitochondrial complex IV (cytochrome c oxidase (COX)) was found extremely variable in all (mutated and wt) samples suggesting an impairment of mitochondrial cristae in these tumors. In conclusion, tumors from patients with germ line SDH mutations invariably show decreased enzymatic activity and content, but an SDH impairment may also depend on SDH somatic mutations or, seemingly, on MAX mutations. The impaired SDH activity in the two wt tissues suggests mutations in other still unknown susceptibility genes. Finally, the extreme variability in COX expression levels is yet to be explained and this strongly suggests to evaluate other mitochondrial features to better understand the mitochondrial role in the pathogenesis of these tumors.

Occurrence of medullary thyroid carcinoma, bronchial carcinoid tumor, and papillary thyroid carcinoma in a family bearing the RET G691S polymorphism

RET mutations play an important role in the development of human neuroendocrine tumors. The prevalence of the RET polymorphism G691S of exon 11 is higher in patients with medullary thyroid carcinoma (MTC) as compared to the general population. A weak association between RET polymorphisms and sporadic papillary thyroid carcinoma (PTC) has also been described. We hereby describe the association of MTC, bronchial carcinoid tumor, and PTC in a familial setting. A 75-yr-old woman developed MTC 7 yr after successful treatment of a bronchial carcinoid. Serum calcitonin was 12.9 pg/ml with a peak response to pentagastrin (151.0 pg/ml). The patient underwent total thyroidectomy and a genetic mutational analysis of the RET gene. Histological evaluation confirmed MTC with no evidence of lymph nodes involvement. After thyroidectomy serum calcitonin was <2.0 pg/ml. A germline missense mutation at codon 691 in exon 11 of the RET gene was found. The mutational analysis was extended to the patient's offspring, and her daughter was found to bear the G691S polymorphism of RET. Wild type RET gene was found in the son. The daughter, who showed a nodular goiter, autoimmune thyroiditis and normal serum calcitonin, also underwent thyroidectomy. Histologic examination of the thyroid revealed an incidental PTC. This is the first description of a bronchial carcinoid tumor occurring in association with MTC. The occurrence of apparently unrelated NET in the same subject, or within a family, should be regarded as a challenge for deeper investigations into the possible oncogenic role of this genetic alteration.

Malignant extra-adrenal pheochromocytoma caused by an SDHB intronic variation leading to a 54-bp deletion in exon 4

In the last few years several papers have reported on the association between mutations of the genes encoding the structural (SDHC, SDHD) and catalytic (SDHB) subunits of succinate dehydrogenase and the occurrence of hereditary pheochromocytomas/paragangliomas (Pheo/PGL) syndromes. We diagnosed a malignant extraadrenal Pheo in a 38-yr-old man with abdominal lesions; many areas of increased uptake at octreoscan scintigraphy in the skeleton indicated metastatic disease. We then approached genetic analysis through the screening of the SDHB, SDHC, and SDHD genes. Here we report a heterozygous G>A transversion at position +1 of intron 4 of SDHB gene. To clarify this mutation we performed cDNA analysis by RT-PCR and we assume that the splice site mutation in intron 4 abolishes the consensus splice donor sequence leading to an in-frame deletion of 18 amino acid. This finding indicates once again that SDHB mutations could predispose to malignant Pheo.

The Y606C RET mutation causes a receptor gain of function

CONTEXT

Medullary thyroid carcinoma (MTC) is the most common feature of multiple endocrine neoplasia type 2A (MEN2A) and occurs in almost all patients affected by germline RET mutations.

OBJECTIVE

We identified and characterized an activating germline RET point mutation (G>A substitution leading to the heterozygous missense mutation Y606C in exon 10), in a 58-year-old female affected by MTC.

DESIGN

The RET/Y606C and RET/C620Y, obtained by site-directed mutagenesis, as well as the RET/wild-type (wt) were cloned in an expression vector and transiently transfected in NIH3T3 fibroblasts. In vitro cell model was used to evaluate the effect of Y606C mutation on the RET downstream signalling pathways through Western blot analysis.

RESULTS

We found that the cysteine insertion, due to the Y606C mutation, results in increased receptor dimerization, which is accompanied by an increased tyrosine phosphorylation of the Y905 residue in the RET/Y606C, demonstrating that the Y606C mutation is associated with constitutive receptor activation. As RET activation results in an intracellular signalling cascade involving extracellular signal-regulated kinases (ERKs), we investigated ERK activity in our transfected cells. Results demonstrated a significant increase in ERK2 phosphorylation in the RET/Y606C vs. the RET/wt and RET/C620Y transfected cells, suggesting an up-regulation of RET signalling.

CONCLUSIONS

All these findings demonstrate that the Y606C mutation is associated with RET constitutive activation and thus has to be considered of pathogenetic relevance in the development of MTC.

Genetics and biology of pheochromocytoma

The familial forms of pheochromocytoma have recently been demonstrated to be more frequent than believed in the past. The genes currently known to be responsible for tumor formation are RET, VHL, NF1, SDHB, SDHC and SDHD. Germline mutations of these genes increase the risk of developing pheochromocytomas and/or paragangliomas which variably associate with other neoplasms and characterize diverse clinical syndromes such as MEN 2, von Hippel-Lindau (VHL), and neurofibromatosis type 1 (NF 1), or the PGL syndromes, respectively. Although the pathogenesis of pheochromocytoma/paraganglioma formation is still largely unknown, studies of the familial forms have started to uncover some pathways that favor tumor formation, such as activation of tyrosine-kinase, induction of hypoxia-inducible factors, activation of the oncogene Ras or reduced apoptosis. These studies have also demonstrated that various gene mutations can differently affect the biological characteristics of pheochromocytoma: for example, while the tumors are mostly adrenergic (epinephrine secreting) and episodically secreting in MEN 2, they are mostly noradrenergic (norepinephrine secreting) and continuously secreting in VHL. Biological variability can also be observed in the PGL syndromes where tumors develop in the head and neck and are parasympathetic in origin and non-secreting, or in the thorax and the abdomen, where they are sympathetic in origin and catecholamine secreting. Genetic testing in patients with pheochromocytomas or paragangliomas is, at present, strongly recommended and is mandatory in young patients or in cases of multiple or recurrent tumors. The clinical picture and the biological characteristics of the tumor may suggest the priority of the genes to be tested first.

Genetic screening for pheochromocytoma: should SDHC gene analysis be included?

PGL3 syndrome is caused by mutations in the SDHC gene. At present, only a few families affected by SDHC mutations have been reported in the literature and in each of them the clinical presentation was characterised by paragangliomas located only in the head and neck regions. No evidence of thoracic or abdominal catecholamine-secreting chromaffin tumours has been reported to date. We report the case of a 15-year-old girl with hypertension and a norepinephrine-secreting abdominal paraganglioma who was found to harbour a novel nonsense SDHC mutation, demonstrating that the clinical presentation of PGL3 syndrome can be more diverse than expected.

SDH Mutations in Patients Affected by Paraganglioma Syndromes: A Personal Experience

Mutations in genes encoding mitochondrial succinate dehydrogenase (SDH) are frequently involved in the development of neural crest-derived (NCD) tumors, such as pheochromocytomas (PHEOs) or paragangliomas (PGLs). In this study we report the results of sequencing analysis in leukocyte DNA of patients affected by PHEO/PGL who turned out to be SDH mutation carriers. A nonsense germline heterozygous mutation (Q109X) was found in the exon 4 of the SDHD gene in the index cases of six unrelated families affected by PHEO/PGL. Haplotype analysis showed the presence of a founder effect. Affected patients showed high clinical variability, ranging from monolateral to bilateral glomus tumors, variably associated or not with PGLs or PHEOs. A novel missense SDHD variant, T112I, was also found in one of our families. A new missense G106D mutation, involving a highly conserved amino acid, was found in two sisters affected by bilateral glomus tumors. A P81L mutation associated with abdominal and head and neck PGL was detected in three families. A G12S variant of the SDHD gene was found in one patient affected by a PHEO. The finding of this variant in 3 of 100 control subjects suggests that it is a polymorphism and not a mutation. A novel IVS2-1G>T variant was found at intron 2 of SDHD gene in one patient affected by a glomus tumor. All the tumors associated with SDHD mutations were benign. Conversely, the only mutation we found in SDHB gene (IVS3+1G>A) was associated with a malignant PHEO.

Phenotype variability of neural crest derived tumours in six Italian families segregating the same founder SDHD mutation Q109X

BACKGROUND

Mutations in genes coding for the mitochondrial complex II succinate dehydrogenase (SDH) subunits cause familial neural crest derived (NCD) tumours.

METHODS

Index cases from six apparently unrelated families affected by NCD tumours were analysed for mutations in the SDHB, SDHC, and SDHD genes.

RESULTS

The same nonsense germline heterozygous mutation (Q109X) in exon 4 of the SDHD gene was found in each of the six families. Overall, 43 heterozygotes were identified. These were evaluated for the presence of NCD tumours through radiological examination of the neck, thorax, and abdomen, and measurement of urinary metanephrines and plasma chromogranin A. A novel missense SDHD variant, T112I, which did not segregate with the Q109X mutation and was not associated with phenotypic manifestations, was observed in one of the families. Microsatellite analysis showed a common haplotype in all individuals heterozygous for the Q109X mutation, indicating a founder effect. Overall, 18 heterozygotes were clinically affected by at least one NCD tumour. Every affected patient inherited the germline mutation from the father, confirming SDHD maternal genomic imprinting. Penetrance of the paternally inherited mutation progressively increased from 33% to 83% at 30 and 60 years, respectively. Affected patients showed high clinical variability, ranging from monolateral to bilateral glomus tumours variably associated or not with paragangliomas or phaeochromocytomas. Loss of heterozygosity was observed in tumour cells isolated by laser capture microdissection.

CONCLUSIONS

This study shows that a single founder SDHD mutation is present in an area of central Italy and that this mutation is associated with widely variable interfamilial and intrafamilial expressivity.

Unique association of non-functioning pheochromocytoma, ganglioneuroma, adrenal cortical adenoma, hepatic and vertebral hemangiomas in a patient with a new intronic variant in the VHL gene

We analyzed the clinical, hormonal, immunohistochemical and genetic features in a 69-yr-old Caucasian woman with a very rare "composite and mixed pheochromocytoma". This was characterized by right adrenal pheochromocytoma associated with homolateral ganglioneuroma and controlateral adrenal cortical adenoma. The three tumors, incidentally discovered, proved to be non-functioning (normal secretion of catecholamines and of other neuroendocrine peptides, glucocorticoids, mineralcorticoids and androgens). Accordingly, the patient showed no sign or symptom of endocrine disease. Computed tomography (CT) and magnetic resonance (MR) demonstrated a typical adenomatous lesion on the left adrenal gland with precocious uptake of the radiotracer on radioidine (131I)-norcholesterol adrenal scintigraphy, while the controlateral gland showed hyperdensity on CT, hyperintensity on MR and no uptake at adrenal scintigraphy. In addition, CT and MR revealed a vertebral and two hepatic hemangiomas. The right adrenal gland was surgically removed and, microscopically, pheochromocytoma and ganglioneuroma areas appeared intermixed without a predominant component. The former showed strong immunoreactivity for chromogranin, synaptophysin, vascular endothelial growth factor (VEGF) and CD34, while the latter appeared positive for neuron-specific enolase (NSE) and S-100. Peripheral blood genomic DNA analysis revealed a new intronic variant (5557A > G) in the von Hippel-Lindau gene (VHL) not observed in our control population.

Multigenic control of serum adiponectin levels: evidence for a role of the APM1 gene and a locus on 14q13

Adiponectin is a circulating enhancer of insulin action that is secreted by the adipose tissue. In epidemiological studies, serum levels of this protein predict the risk of type 2 diabetes and cardiovascular events. Serum adiponectin levels have been associated with variants at the adiponectin (APM1) and PPARgamma2 loci and have also been linked to markers on 5p15 and 14q13. We investigated the role of these four loci in regulating serum adiponectin in a Caucasian population from Italy. Four haplotype-tagging single-nucleotide polymorphisms (ht-SNPs) (-11377 C>G, -4041 A>C, +45 T>G, and +276 G>T) at the APM1 locus and the PPARgamma2 Pro12Ala polymorphism were examined for association with serum adiponectin in 413 unrelated, nondiabetic individuals. Of the five SNPs tested, +276G>T was the only one to be associated with serum adiponectin (P = 0.032), with "TT" individuals having higher adiponectin levels than other subjects. In a variance-components analysis of 737 nondiabetic members of 264 nuclear families, adiponectin heritability was 30%, with a small but significant proportion explained by the +276 genotype ( P = 0.0034). Suggestive evidence of linkage with adiponectin levels was observed on chromosome 14q13, with a LOD of 2.92 (P = 0.000057) after including the APM1 +276 genotype in the model. No linkage was observed at 5p15. Our data indicate a strong genetic control of serum adiponectin. A small proportion of this can be attributed in our population to variability at the APM1 locus, but an as yet unidentified gene on 14q13 appears to play a much bigger role.

Insulin modulates PC-1 processing and recruitment in cultured human cells

We evaluated whether insulin signaling modulates plasma cell glycoprotein (PC-1) plasma membrane recruitment, posttranslational processing, and gene expression in human cultured cell lines. Insulin induced a fourfold increase (P < 0.01) of membrane PC-1 expression by rapid and sensitive mechanism(s). This effect was reduced (P < 0.05-0.01) by inhibition of phosphatidylinositol 3-kinase (200 nmol/l wortmannin) and S6 kinase (50 nmol/l rapamycin) activities and intracellular trafficking (50 micromol/l monensin) and was not accompanied by PC-1 gene expression changes. Moreover, at Western blot, insulin elicited the appearance, in both plasma membrane and cytosol, of a PC-1-related 146-kDa band (in addition to bands of 163, 117, 106, and 97 kDa observed also in absence of insulin) that was sensitive to endoglycosidase H. Finally, inhibition of PC-1 translocation to plasma membrane, by wortmannin pretreatment, increases insulin-stimulated receptor autophosphorylation. Our data indicate that insulin stimulates PC-1 posttranslational processing and translocation to the plasma membrane, which in turn impairs insulin receptor signaling. Bidirectional cross talk between insulin and PC-1, therefore, takes place, which may be part of the hormone self-desensitization mechanism.

A cluster of three single nucleotide polymorphisms in the 3'-untranslated region of human glycoprotein PC-1 gene stabilizes PC-1 mRNA and is associated with increased PC-1 protein content and insulin resistance-related abnormalities

Glycoprotein PC-1 inhibits insulin signaling and, when overexpressed, plays a role in human insulin resistance. Mechanisms of PC-1 overexpression are unknown. We have identified a haplotype in the 3'-untranslated region of the PC-1 gene that may modulate PC-1 expression and confer an increased risk for insulin resistance. Individuals from Sicily, Italy, carrying the "P" haplotype (i.e., a cluster of three single nucleotide polymorphisms: G2897A, G2906C, and C2948T) were at higher risk (P < 0.01) for insulin resistance and had higher (P < 0.05) levels of plasma glucose and insulin during an oral glucose tolerance test and higher levels of cholesterol, HDL cholesterol, and systolic blood pressure. They also had higher (P < 0.05-0.01) PC-1 protein content in both skeletal muscle and cultured skin fibroblasts. In CHO cells transfected with either P or wild-type cDNA, specific PC-1 mRNA half-life was increased for those transfected with P (t/2 = 3.73 +/- 1.0 vs. 1.57 +/- 0.2 h; P < 0.01). In a population of different ethnicity (Gargano, East Coast Italy), patients with type 2 diabetes (the most likely clinical outcome of insulin resistance) had a higher P haplotype frequency than healthy control subjects (7.8 vs. 1.5%, P < 0.01), thus replicating the association between the P allele and the insulin resistance-related abnormalities observed among Sicilians. In conclusion, we have identified a possible molecular mechanism for PC-1 overexpression that confers an increased risk for insulin resistance-related abnormalities.

High insulin levels do not influence PC-1 gene expression and protein content in human muscle tissue and hepatoma cells

BACKGROUND

To verify whether insulin levels influence PC-1 tissue content, we studied PC-1 gene expression and protein content in skeletal muscle of patients with insulinoma, a model of primary hyperinsulinemia. Data were compared with those obtained in matched insulin sensitive or resistant healthy subjects. In addition, the effect of high insulin concentration on PC-1 protein content was studied in HepG2 cells.

METHODS

The following measurements were performed: insulin sensitivity by euglycemic clamp; PC-1 protein content and insulin receptor autophosphorylation by specific ELISAs; PC-1 gene expression by competitive polymerase chain reaction (PCR); phosphatidyl-inositol-3 kinase by immunoprecipitation and thin layer chromatography; glycogen synthesis by (14)C-glucose incorporation.

RESULTS

Muscle PC-1 content was similar in the insulinoma patients and in insulin sensitive controls but higher (p<0.01) in insulin resistant controls (21.9+/-4.6 ng/mg protein, 23.8+/-3.9, 48.0+/-8.7, respectively). PC-1 protein content was inversely correlated with insulin sensitivity (r=-0.5, p<0.015) but with neither plasma insulin nor glucose levels. PC-1 protein content was correlated with PC-1 gene expression (r=0.53, p<0.05, n=14). Exposure to high insulin (100 nmol/l for 16 h) caused a significant (p<0.05-0.01) impairment of insulin receptor autophosphorylation, phosphatidyl-inositol-3 kinase activity and glycogen synthesis, but not of PC-1 protein content (114+/-3 vs 102+/-14 ng/mg protein) in HepG2 cells.

CONCLUSION

These findings suggest that chronic high insulin levels do not influence PC-1 expression.

A polymorphism (K121Q) of the human glycoprotein PC-1 gene coding region is strongly associated with insulin resistance

The genes responsible for insulin resistance are poorly defined. Plasma cell differentiation antigen (PC-1) glycoprotein inhibits insulin receptor signaling and is associated with insulin resistance. We describe here a novel polymorphism in exon 4 of the PC-1 gene (K121Q) and demonstrate that it is strongly associated with insulin resistance in 121 healthy nonobese (BMI <30 kg/m2) nondiabetic (by oral glucose tolerance test [OGTT]) Caucasians from Sicily. Compared with 80 KK subjects, Q allele carriers (n = 41, 39 KQ and 2 QQ) showed higher glucose and insulin levels during OGTT (P < 0.001 by two-way analysis of variance) and insulin resistance by euglycemic clamp (M value = 5.25 +/- 1.38 [n = 24] vs. 6.30 +/- 1.39 mg x kg(-1) x min(-1) [n = 49], P = 0.005). Q carriers had higher risk of being hyperinsulinemic and insulin resistant (odds ratio [CI]: 2.99 [1.28-7.0], P < 0.001). Insulin receptor autophosphorylation was reduced (P < 0.01) in cultured skin fibroblasts from KQ versus KK subjects. Skeletal muscle PC-1 content was not different in 11 KQ versus 32 KK subjects (33 +/- 16.1 vs. 17.5 +/- 15 ng/mg protein, P = 0.3). These results suggest a cause-effect relationship between the Q carrying genotype and the insulin resistance phenotype, and raise the possibility that PC-1 genotyping could identify individuals who are at risk of developing insulin resistance, a condition that predisposes to type 2 diabetes and coronary artery disease.