Pancreatic endocrine tumours: evidence for a tumour suppressor pathogenesis and for a tumour suppressor gene on chromosome 17p

Two molecular pathways leading to cancer are known. Common-type cancers arise from the 'tumour suppressor' pathway, characterized by gross chromosomal changes and allelic losses (LOH) in an average of 25 per cent or more of randomly chosen chromosomal loci. The 'mutator pathway' has been recognized in a subset of cancers, characterized by widespread microsatellite DNA instability and rarity of chromosomal losses. The present study has investigated 20 pancreatic endocrine tumours (PETs) for loss of heterozygosity (LOH) at seven chromosomal loci (3p14, 7q31-32, 11q13, 13q14, 18q21, 17p13, and 17q21); microsatellite instability; and Ki-ras, N-ras, and p53 gene mutations. LOH was found in an average of 24 per cent of the chromosomal loci analysed. No tumour showed microsatellite instability. Ki-ras and p53 mutations were each found in one case. The frequency of losses was higher in malignant (40 per cent) than in benign (17 per cent) tumours (p = 0.009), and the specific chromosome 17p13 LOH was associated with extrapancreatic extension of disease (p = 0.007), high proliferative activity (p = 0.001), and absence of progesterone receptors (p = 0.01). A common deleted region on chromosome 17p13 and the rarity of p53 gene mutations suggest the existence of a novel tumour suppressor gene involved in the pathogenesis of PETs in this chromosomal area.

Multiple channels mediate calcium leakage in the A7r5 smooth muscle-derived cell line

Ca2+ entry under resting conditions may be important for contraction of vascular smooth muscle, but little is known about the mechanisms involved. Ca2+ leakage was studied in the A7r5 smooth muscle-derived cell line by patch-clamp techniques. Two channels that could mediate calcium influx at resting membrane potentials were characterized. In 110 mM Ba2+, one channel had a slope conductance of 6.0 +/- 0.6 pS and an extrapolated reversal potential of +41 +/- 13 mV (mean +/- SD, n = 8). The current rectified strongly, with no detectable outward current, even at +90 mV. Channel gating was voltage independent. A second type of channel had a linear current-voltage relationship, a slope conductance of 17.0 +/- 3.2 pS, and a reversal potential of +7 +/- 4 mV (n = 9). The open probability increased e-fold per 44 +/- 10 mV depolarization (n = 5). Both channels were also observed in 110 mM Ca2+. Noise analysis of whole-cell currents indicates that approximately 100 6-pS channels and 30 17-pS channels are open per cell. These 6-pS and 17-pS channels may contribute to resting calcium entry in vascular smooth muscle cells.

Prompt hepatitis C virus suppression following hepatitis B virus superinfection in chronic untreated hepatitis C

The natural course of chronic hepatitis C virus infection after hepatitis B virus superinfection is not clear since it is difficult to determine the chronology of the double infections. We report on a case of de novo hepatitis B virus infection in the course of chronic untreated hepatitis C, in which the time of hepatitis B virus infection is actually known. The patient eliminated HCV-RNA, both from serum and from liver tissue, soon after the clinical onset of the acute hepatitis B. Liver histology featured hepatitis with severe portal inflammation and high-grade periportal and intralobular necro-inflammatory lesions. This observation demonstrates that hepatitis C virus replication can be promptly and spontaneously suppressed by acute hepatitis B virus superinfection.

PKC activity modulates availability and long openings of L-type Ca2+ channels in A7r5 cells

The possibility that protein kinase C (PKC) could control the activity of L-type Ca2+ channels in A7r5 vascular smooth muscle-derived cells in the absence of agonist stimulation was investigated using the patch-clamp technique. Consistent with the possibility that L-type Ca2+ channels are maximally phosphorylated by PKC under these conditions, we show that 1) activation of PKC with the phorbol ester phorbol 12,13-dibutyrate was ineffective in modulating whole cell and single-channel currents, 2) inhibition of PKC activity with staurosporine or chelerythrine inhibited channel activity, 3) inhibition of protein phosphatases by intracellular dialysis of okadaic acid did not affect whole cell currents, and 4) the inhibitory effect of staurosporine was absent in the presence of okadaic acid. The inhibition of Ca2+ currents by PKC inhibitors was due to a decrease in channel availability and long open events, whereas the voltage dependence of the open probability and the single-channel conductance were not affected. The evidence suggests that in resting, nonstimulated A7r5 cells there is a high level of PKC activity that modulates the gating of L-type Ca2+ channels.

A high copy suppressor screen reveals genetic interactions between BET3 and a new gene. Evidence for a novel complex in ER-to-Golgi transport

The BET3 gene in the yeast Saccharomyces cerevisiae encodes a 22-kD hydrophilic protein that is required for vesicular transport between the ER and Golgi complex. To gain insight into the role of Bet3p, we screened for genes that suppress the growth defect of the temperature-sensitive bet3 mutant at 34 degrees. This high copy suppressor screen resulted in the isolation of a new gene, called BET5. BET5 encodes an essential 18-kD hydrophilic protein that in high copy allows growth of the bet3-1 mutant, but not other ER accumulating mutants. This strong and specific suppression is consistent with the fact that Bet3p and Bet5p are members of the same complex. Using PCR mutagenesis, we generated a temperature-sensitive mutation in BET5 (bet5-1) that blocks the transport of carboxypeptidase Y to the vacuole and prevents secretion of the yeast pheromone alpha-factor at 37 degrees. The precursor forms of these proteins that accumulate in this mutant are indicative of a block in membrane traffic between the ER and Golgi apparatus. High copy suppressors of the bet5-1 mutant include several genes whose products are required for ER-to-Golgi transport (BET1, SEC22, USO1 and DSS4) and the maintenance of the Golgi (ANP1). These findings support the hypothesis that Bet5p acts in conjunction with Bet3p to mediate a late stage in ER-to-Golgi transport. The identification of mammalian homologues of Bet3p and Bet5p implies that the Bet3p/Bet5p complex is highly conserved in evolution.

Molecular approach in human tumor investigation: oncogenes, tumor suppressor genes and DNA tumor polyomaviruses (review)

Molecular analysis are useful for diagnosis, prognosis and follow-up of the patients, as well as for addressing therapeutic choices. Most of the molecular methods are based on the analysis of nucleic acids. The DNA and RNA methodologies of routine applicability include Southern and Northern hybridizations and polymerase chain reaction (PCR) techniques. Southern blot hybridization recognizes major DNA rearrangements, and detection of oncogenic viral sequences present in high copy number, whereas PCR-based methods allow the detection of gross chromosomal modifications, fine gene alterations and low amount of tumor virus footprints. PCR techniques also allow the analysis of the partially degraded nucleic acids from formalin-fixed paraffin-embedded tissues. We present an overview of the use of molecular techniques for the analysis, diagnosis, prognosis and follow-up of neoplastic diseases, using examples from our experience in both leukemias and solid tumors.

Pancreatic carcinoma: correlation between E-cadherin and alpha-catenin expression status and liver metastasis

BACKGROUND

Dysfunction of the E-cadherin/catenin-mediated cell-cell adhesion system has been associated with invasiveness and poor differentiation of human carcinomas. However, its importance in the genesis of liver metastasis has not been examined sufficiently.

METHODS

A series of 26 primary pancreatic carcinomas and the concomitant liver metastases from 15 of them, obtained at autopsy, were analyzed for E-cadherin and alpha-catenin protein expression by immunohistochemistry.

RESULTS

Both E-cadherin and alpha-catenin expression were preserved in 15 (58%) and reduced in 11 (32%) of the 26 primary pancreatic carcinomas. In the former 15 primaries, carcinoma cells were attached to each other tightly, whereas the latter 11 primaries showed isolated or loosely connected attachments. The metastatic ratio was higher in tumors exhibiting tight adhesion than in those with loose adhesion: 73% and 36%, respectively (P = 0.059). E-cadherin and alpha-catenin expression patterns in liver metastases basically followed those in the corresponding primaries (P < 0.01).

CONCLUSIONS

Reduced E-cadherin and alpha-catenin expression in primary pancreatic carcinoma has no significant predictive value regarding the presence of liver metastasis. Rather, there is a greater tendency for liver metastasis in cases in which the integrity of the E-cadherin/catenin-mediated cell-cell adhesion system is intact.

Clonality of B-cells in portal lymphoid infiltrates of HCV-infected livers

Evidence has been accumulating in favour of a role for hepatitis C virus (HCV) in the pathogenesis of human lymphoproliferative disorders. HCV infection has been documented in the majority of patients with essential mixed cryoglobulinaemia type II (MC-II); in patients with HCV infection, B-cell clonal expansion have been detected in peripheral blood and bone marrow, and a high prevalence of B-cell non-Hodgkin's lymphomas has been documented. Liver biopsies in chronic hepatitis C frequently show portal lymphoid infiltrates with features of B follicles, whose clonality has not yet been investigated. This study has analysed the B-cell clonality of portal lymphoid infiltrates from 16 patients with chronic HCV hepatitis. Portal tracts showing obvious lymphoid infiltrates were microdissected from the paraffin-embedded liver tissue sections and the clonality of lymphoid B-cells was tested using a polymerase chain reaction (PCR) approach designed to identify immunoglobulin heavy chain gene (IgH) rearrangements. A successful IgH-PCR analysis was achieved in 35 lymphoid infiltrates from 11 patients (seven with the four without MC-II) and yielded a single band in 21 cases, two bands in ten cases, and three bands in four cases. Comparison of the IgH-PCR amplification bands obtained from the different lymphoid aggregates of the same biopsy revealed that they differed in size. This finding indicates that each aggregate derives from the proliferation of one or a few founder B-cells, which are not related to each other. The results obtained in patients with and without MC-II were similar, suggesting that the presence of B-cell clonal proliferations in liver biopsies is independent of the occurrence of B-cells producing monoclonal IgMk cryoglobulins.

TRAPP, a highly conserved novel complex on the cis-Golgi that mediates vesicle docking and fusion

We previously identified BET3 by its genetic interactions with BET1, a gene whose SNARE-like product acts in endoplasmic reticulum (ER)-to-Golgi transport. To gain insight into the function of Bet3p, we added three c-myc tags to its C-terminus and immunopurified this protein from a clarified detergent extract. Here we report that Bet3p is a member of a large complex ( approximately 800 kDa) that we call TRAPP (transport protein particle). We propose that TRAPP plays a key role in the targeting and/or fusion of ER-to-Golgi transport vesicles with their acceptor compartment. The localization of Bet3p to the cis-Golgi complex, as well as biochemical studies showing that Bet3p functions on this compartment, support this hypothesis. TRAPP contains at least nine other constituents, five of which have been identified and shown to be highly conserved novel proteins.

Molecular pathogenesis of sporadic duodenal cancer

Whether duodenal adenocarcinoma should be considered as a gastrointestinal or as a peripancreatic cancer is a matter of debate, as is the opportunity and type of treatment. We investigated 12 such cancers for the genetic anomalies involved in the pathogenesis of gastrointestinal malignancies, including (a) those occurring in common-type cancers - allelic losses at chromosomes 3p, 5q, 17p and 18q, and Ki-ras and p53 alterations; and (b) those characteristic of mutator-phenotype cancers - microsatellite instability and TGF-betaRII gene mutations. We found Ki-ras and p53 mutations in five (42%) and eight cancers (67%), respectively; chromosome 3p, 5q, 17p and 18q allelic losses in two of nine (22%), six of ten (60%), six of nine (67%) and three of ten (30%) informative cancers, respectively. Finally, three cancers (25%) showed widespread microsatellite instability and two of them had a TGF-betaRII gene mutation. Our data suggest that duodenal cancers may arise from either of the two known pathogenetic molecular pathways of gastric and colorectal cancers. The majority of our cases were highly aggressive cancers with frequent chromosomal changes and p53 mutations as observed in the common-type gastrointestinal malignancies, while widespread subtle alterations characteristic of mutator-phenotype cancers occurred in a minority, which also showed a favourable long-term outcome.

Molecular techniques in hematopathology

Molecular techniques have already earned a place in the management of hematologic disorders. The requests of clinical hematologists to Pathology include, besides the diagnosis, any additional information useful for prognosis and therapeutic choices, as well as expertise and technologies to follow-up patients. To fulfill these commitments, pathologists have been resorting to classical morphology, cytochemistry, immunocytochemistry, and have only recently come to include molecular genetic techniques. Most of the molecular methods of practical utility are based on the analysis of DNA. The DNA methodologies of routine applicability mainly include Southern blotting and polymerase chain reaction (PCR). Southern blotting recognizes major DNA rearrangements, whereas PCR-based methods allow to recognize both gross chromosomal modifications and fine gene alterations, including point mutations. PCR techniques may also be used for partially degraded DNA from formalin-fixed paraffin-embedded tissues. Here we will draw a brief overview of the role of molecular genetic techniques in the pathology practice for the diagnosis, prognosis and follow-up of neoplastic diseases, using examples from our experience.

Cancers of the papilla of vater: mutator phenotype is associated with good prognosis

Cancer of the papilla (ampulla) of Vater is an uncommon disease that kills 60% of affected patients. There is general agreement that local spread of the tumor (T stage) is the only significant and independent prognostic factor for this cancer, whereas the predictive value of tumor grade and lymph node metastases is controversial. The genetic anomalies involved in this process have the potential to serve as additional prognostic markers. We explored 25 ampullary cancers for the occurrence of instability at simple repeat DNA sequences (microsatellites) of the type seen in replication error phenotype (RER-positive) cancers. Ten microsatellites from five different chromosomes were amplified by PCR from both normal and cancer tissue DNA of the same patients. A tumor was defined as RER-positive when microsatellite instability was found in the majority (>/=6) of the loci analyzed. Five cancers (20%) showed a RER phenotype and were associated with long survival of patients (32-96 months), whereas RER-negative cancers had a significantly poorer prognosis (Mantel-Cox test; P = 0.0084), with a median actuarial survival of 17 months. We also report that three (12%) patients belonged to cancer-prone families and four (16%) were cancer-prone individuals.

Heart rate and skin conductance in behaviorally inhibited Mauritian children

This study tested predictions that inhibited versus uninhibited children exhibit higher heart rate (HR) and skin conductance (SC) arousal. Mauritian children (N = 1,795) were tested at age 3 and classified as inhibited, middle, or uninhibited on the basis of social behavior. HR level and several SC measures were obtained immediately before or during a tone task. Inhibited children displayed significantly higher HR and SC levels and longer SC latency relative to uninhibited children. Results remained regardless of ethnicity, gender, height, weight, respiratory complaints, or crying behavior. Findings suggest that HR and SC levels may be early indicators of inhibited or uninhibited behavior at age 3 and support the notion of heightened sympathetic reactivity due to limbic arousal in inhibited children.

Psychophysiology of anger and violent behavior

Antisocial behavior is a complex phenomenon that arises out of multiple causes involving biologic, psychological, and social forces. Moreover, different forms of violent antisocial behavior may each result from different biopsychosocial pathways. The overview of human psychophysiologic findings presented in this article provides some support for this notion. In particular, the finding of psychophysiologic underarousal (e.g., reduced resting HR and SC levels, increased slow-wave EEG, poor classical conditioning) is one of the most robust and best replicated findings in antisocial populations. The majority of these studies consist of populations exhibiting nonviolent antisocial behavior or milder forms of aggression. Findings of underarousal in institutionalized criminal samples are very few in number and are not well-replicated. The relationship of psychophysiologic underarousal to antisocial behavior, therefore, may be specific to covert forms of antisocial behavior and perhaps to some less severe forms of violent behavior. On the other hand, violence associated with anger and emotional aggression (which is often more impulsive, less controlled, and reactive to some perceived provocation) may have very different psychophysiologic underpinnings. It was suggested that risk factors for emotional aggression include a predisposition to negative affect/arousal and an inability to regulate that affect/arousal. It also was suggested that this effect will be most pronounced in individuals experiencing stressors or adverse social environments, where negative affect and arousal would be increased. Laboratory studies have suggested that overarousal may facilitate aggression in situations in which someone has been provoked. Clinical studies also have indicated a relationship between increased physiologic arousal, negative emotionality, and aggression/antisocial behavior in some populations, with increases in aggression in those also exposed to adverse home environments. Thus, the relationship of increased psychophysiologic arousal to antisocial behavior may be more specific to angry or emotional violence. It is important to note that these psychophysiologic distinctions are speculative for few studies actually have differentiated type of violence in their design. Pitts did group children according to proactive or reactive aggression and found reduced HR levels in both groups, but a substantial increase in HR only in the reactive aggressive group. Lakosina and Trunova found increased SC responsivity in psychopathic individuals characterized by affective violence. These studies provide some initial support for underarousal in proactive/instrumental aggression and overarousal in emotional aggression. It is important, however, that more studies be done with subtypes of violence to test the notion of such differential psychophysiologic patterns. Lastly, some definitional and methodologic considerations need to be mentioned. First, a distinction exists between physiologic arousal and reactivity. Typically, arousal refers to psychophysiologic activity that occurs during a resting state, whereas reactivity refers to activity that occurs in response to some stimulus. Although some studies did assess measures during a resting state, the majority of findings on over-arousal in relation to emotional aggression more accurately reflect psychophysiologic and emotional reactivity to a situation or stimulus. Second, arousal or reactivity are nonspecific terms that can refer to any psychophysiologic response system (e.g., electrodermal, cardiovascular, cortical, and so on). Responses from these systems typically do not correlate in the general population. Thus, it would be worthwhile for future studies to include more than one response system (as done by Raine et al) and see if the arousal/reactivity measures converge. If the measures converge, a general model of arousal or reactivity is supported. (ABSTRACT TRUNCATED)

The human ALL-1/MLL/HRX antigen is predominantly localized in the nucleus of resting and proliferating peripheral blood mononuclear cells

The ALL-1 gene is an important regulator of embryonal and hematopoietic development, and structural variants of the human gene generated by chromosomal translocations and other genomic alterations presumably act as oncogenes in the pathogenesis of acute leukemias and other hematological malignancies. Antisera against two different epitopes of the human ALL-1 protein (anti-ALL1-N and anti-ALL1-C) were produced. Both sera revealed indistinguishable patterns of antigen localization in human peripheral blood mononuclear cells (PBMCs). In resting PBMCs, the antigen was distributed in a speckled pattern across the nuclei, with an increased density at the nuclear envelope and the nuclear indentation. In mitotically stimulated PBMCs, the antigen surrounded the condensing chromosomes but did not colocalize with chromatin or the nuclear scaffold. The antigen is considered a marker for a novel nuclear subcompartment, a perichromosomal area termed the "chromosomal envelope." In Western blot experiments, the anti-ALL1-N serum reacted with a polypeptide corresponding to the expected full-length 430-kDa ALL-1 protein. Recombinant proteins representing the AT-hook and zinc binding subdomains of the ALL-1 protein interacted in vitro with a degenerate mixture of double-stranded oligodeoxynucleotides. Thus, the ALL-1 protein probably is a DNA-binding protein with both a sequence-unspecific (AT-hook) and a sequence-specific (zinc binding subdomains) double-stranded DNA binding mode.

Heart rate and skin conductance in behaviorally inhibited Mauritian children

This study tested predictions that inhibited versus uninhibited children exhibit higher heart rate (HR) and skin conductance (SC) arousal. Mauritian children (N = 1,795) were tested at age 3 and classified as inhibited, middle, or uninhibited on the basis of social behavior. HR level and several SC measures were obtained immediately before or during a tone task. Inhibited children displayed significantly higher HR and SC levels and longer SC latency relative to uninhibited children. Results remained regardless of ethnicity, gender, height, weight, respiratory complaints, or crying behavior. Findings suggest that HR and SC levels may be early indicators of inhibited or uninhibited behavior at age 3 and support the notion of heightened sympathetic reactivity due to limbic arousal in inhibited children.

Abnormal orienting in schizotypal personality disorder

Previous studies have found evidence for skin conductance (SC) orienting abnormalities in psychosis-prone subjects, but there have been no previous studies on subjects with a diagnosis of schizotypal personality disorder. This study assesses whether clinical schizotypal subjects show abnormal habituation to orienting stimuli. Thirteen subjects with both high scores on the Schizotypal Personality Questionnaire (SPQ) and a DSM-III-R clinical diagnosis of schizotypal personality disorder were compared to 30 controls with no such diagnosis and with low scores on the SPQ. While normals showed the expected habituation in SC orienting across trials, schizotypal subjects failed to show a decrement in responding across the first three trials. In a second study on 30 new subjects, individual differences in schizotypy correlated significantly (p = 0.47) and in the predicted direction with a dimensional measure of the orienting deficit. It is hypothesized that this retarded habituation in schizotypals reflects a deficit in preattentive template matching, which may in turn partly relate to the working memory and prefrontal deficits observed in schizotypal and schizophrenia patients.

APC gene mutations and allelic losses in sporadic ampullary tumours: evidence of genetic difference from tumours associated with familial adenomatous polyposis

We explored APC gene mutations and chromosome 5q21 allelic losses (5qLOH) in 18 neoplasms of the papilla of Vater, including 6 early-stage tumours (3 adenomas, 3 carcinomas) and 12 advanced-stage cancers. Eleven PCR-amplified polymorphic sequences were used to analyse 5qLOH. APC mutations were investigated both by an in vitro APC-protein truncation test and by single-strand conformation polymorphism analysis. Mutations in the Ki-ras, N-ras and p53 genes were also assessed. We found: 5qLOH in 8 of 16 cases (50%), including 1 adenoma, 3 early- and 4 advanced-stage cancers; APC mutations in 2 adenomas and 1 advanced-stage carcinoma; Ki- or N-ras mutations in 3 adenomas and 3 advanced-stage cancers; p53 mutations in 2 early-stage and 7 advanced-stage adenocarcinomas. Our results suggest that 5qLOH, APC mutations and ras mutations are present at early stages, whereas p53 inactivation is associated with progression of malignancy in a large proportion of cases. These data indicate that sporadic ampullary tumours differ from those occurring in familial adenomatous polyposis in the frequency (17% vs. 64%) as well as in the site of APC somatic mutations, suggesting a different molecular pathogenesis in the 2 conditions.

p21/WAF1 cyclin-kinase inhibitor expression in non-Hodgkin's lymphomas: a potential marker of p53 tumor-suppressor gene function

p21WAF1 (wild-type p53-activated fragment 1) is involved in the control of mammalian cell cycle through the binding and inhibition of cyclin-dependent kinases (Cdk). Because the product of WAF1 gene is a potent downstream effector of the p53 tumor-suppressor gene function, its pattern of cellular expression might correlate with nuclear accumulation of p53-encoded protein and/or p53 gene mutations occurring in malignant lymphomas. To investigate this issue, we analyzed immunohistochemically the expression of p53 and p21WAF1 proteins in tissue involved by non-Hodgkin's lymphomas (NHLs;253 cases) of various histologic types. In a proportion of them (80 cases), we also investigated the possible presence of p53 gene mutations using single-strand conformation polymorphism analysis and direct DNA sequencing. The absence of both p21WAF1 and p53 proteins was observed in 147 of 217 cases (67.7%) among CD30-NHL and in only 8 of 36 (22.2%) CD30+cases, which were mostly anaplastic large-cell lymphomas. A consistent number (> 10%) of p21WAF1-expressing cells was shown in 48 of 253 (18.9%) NHL cases, with a higher incidence in CD30+cases (25/36 [69.4%]), which mostly (21/36) coexpressed p53. These latter cases were characterized by a germline configuration of the p53 gene. In 50 of 253 NHL samples (19.7%), 47 of which (21.6%) belong to the CD30-group, neoplastic cells were p53+/p21-. In all of these cases, the p53+cells accounted for more than 50% of neoplastic cells, up to 100%. Point mutations of p53 gene were solely observed in all investigated cases with this latter phenotype. Our findings strongly suggest that the combined immunohistochemical evaluation of p53 and p21WAF1 is a valuable means of assessing the functional status of the p53 tumor-suppressor gene product in NHL with potential application in the monitorage and prognostication of individual cases.

APC gene mutations and allelic losses in sporadic ampullary tumours: evidence of genetic difference from tumours associated with familial adenomatous polyposis

We explored APC gene mutations and chromosome 5q21 allelic losses (5qLOH) in 18 neoplasms of the papilla of Vater, including 6 early-stage tumours (3 adenomas, 3 carcinomas) and 12 advanced-stage cancers. Eleven PCR-amplified polymorphic sequences were used to analyse 5qLOH. APC mutations were investigated both by an in vitro APC-protein truncation test and by single-strand conformation polymorphism analysis. Mutations in the Ki-ras, N-ras and p53 genes were also assessed. We found: 5qLOH in 8 of 16 cases (50%), including 1 adenoma, 3 early- and 4 advanced-stage cancers; APC mutations in 2 adenomas and 1 advanced-stage carcinoma; Ki- or N-ras mutations in 3 adenomas and 3 advanced-stage cancers; p53 mutations in 2 early-stage and 7 advanced-stage adenocarcinomas. Our results suggest that 5qLOH, APC mutations and ras mutations are present at early stages, whereas p53 inactivation is associated with progression of malignancy in a large proportion of cases. These data indicate that sporadic ampullary tumours differ from those occurring in familial adenomatous polyposis in the frequency (17% vs. 64%) as well as in the site of APC somatic mutations, suggesting a different molecular pathogenesis in the 2 conditions.

Regulation of Mg2+ homeostasis by insulin in perfused rat livers and isolated hepatocytes

Several recent studies demonstrate that adrenergic receptor stimulation evokes marked changes in Mg2+ homeostasis. As insulin counter-regulates many of the metabolic consequences of adrenergic receptor stimulation, we evaluated the potential influence of insulin on Mg2+ movements in response to adrenergic stimulation. The data demonstrate that insulin is able to block the Mg2+ efflux from perfused rat livers stimulated by isoproterenol or 8-Br-cAMP, but has little or no effect on epinephrine or phenylephrine induced Mg2+ efflux. Thus, evidence is provided demonstrating that there are redundant adrenergic pathways regulating Mg2+ efflux from liver tissue. One of these pathways, the beta-adrenergic component, is selectively blocked by insulin. Furthermore, these findings may provide a cellular explanation for hypomagnesemia associated with diabetes.

Expression of MHC class I and class II antigens in pancreatic adenocarcinomas

The antigens encoded by the major histocompatibility complex (MHC) are cell surface glycoproteins that play a fundamental role in the regulation of the immune response. Anomalous MHC expression in tumor cells has been viewed as an important feature to escape tumor recognition by immune cells. Low or absent MHC class I expression as well as ectopic MHC class II expression have been often observed to correlate with high grade malignancy and metastatic potential in a variety of human cancers. To date, very little investigation of MHC (HLA in man) class I and class II expression in human pancreatic cancer has been reported. We investigated this aspect on frozen sections of 8 pancreatic adenocarcinomas and 18 established in vitro cell lines. HLA class I was expressed in all but two cancers whereas de novo HLA class II expression was detected in 3 of 8 cancers. Interestingly, a hierarchy in the expression of the various subsets of HLA class II was found with HLA- DR > -DP > -DQ. Results on cell lines strongly resembled the ones obtained in cancer tissues. However, a peculiar feature was observed in certain cell lines. HLA class II antigens were expressed in only a few cell lines and in some of them a mixed population of positive and negative cells was found. Sorting and cloning of the two populations confirmed the existence of tumor cell clones with stable and distinct HLA class II phenotype. Taken together, these results indicate the cellular heterogeneity of pancreatic cancer cells with regard to the qualitative and quantitative expression of major histocompatibility complex genes, and may provide new insights for a better understanding of the tumorhost relationships in this extremely severe form of neoplasia.

Mg2+ control of respiration in isolated rat liver mitochondria

The role of endogenous mitochondrial Mg2+ as a potential regulator of mitochondrial dehydrogenase activity, and therefore of cellular respiration, was measured in isolated mitochondria containing matrix Ca2+ and Mg2+ levels resembling those occurring in vivo. Ca2+ and Mg2+ depletion was carried out using the cation ionophore A23187 in the presence or absence of the Ca2+ uniporter inhibitor ruthenium red (RR). Divalent cation depletion inhibits the oxidation of alpha-ketoglutarate or pyruvate in states 4 and 3, slows uncoupled respiration and results in decreased membrane potential. Since the addition of Mg2+ could not restore respiration, these dehydrogenases appear not to be regulated by Mg2+. In contrast, similar cation depletion stimulates succinate dehydrogenase (or glutamate dehydrogenase) in state 4 without decreasing membrane potential. The addition of RR caused authentic uncoupling, accompanied by a decrease in membrane potential and an increase in membrane permeability. These effects could be completely reversed by Mg2+. These and other data, showing that Mg2+ depletion results in a change of respiration depending on the substrate oxidized and the metabolic state, indicate that Mg2+ removal may have direct and indirect effects on mitochondrial respiration. A clear direct effect is the stimulation of succinate or glutamate dehydrogenase by decreasing matrix Mg2+. Hence, changes in matrix Mg2+ (in addition to those of Ca2+) could be of great consequence, not only for the control of respiration but also for metabolic pathways affected by changes in concentrations of matrix substrates.