Mentally ill mothers who have killed: three cases addressing the issue of future parenting capability

Many parents with severe and chronic mental illness lose custody of their children due to child abuse or neglect. These children may linger in foster care for long periods of time until decisions about custody are made. Recent proposals to shorten the time that children remain in the foster care system include the use of categories of abuse to guide decisions about custody. One proposal has been to "fast-track" cases involving parents with long-standing mental disorders by automatically terminating parental rights. This approach assumes that a severe and chronic mental disorder is incompatible with safe parenting. This report describes three cases of mentally ill mothers who lost custody of their children after they killed someone. The mothers were nonetheless found to be at low risk for future child maltreatment and violence according to evaluation with two current methodologies, Parenting Risk Assessment and Risk of Violence Assessment. The cases question the assumption that mental illness is incompatible with safe parenting and underscore the fact that evaluation of the parenting competency of mentally ill parents is rarely clear-cut.

Changes in kinesin distribution and phosphorylation occur during regulated secretion in pancreatic acinar cells

In secretory cells, microtubule- (Mt-) based motor enzymes are thought to support transport of secretory vesicles to the cell surface for subsequent release. At present, the role of Mts and kinesin in secretory vesicle transport in exocrine epithelial cells has not been defined. Furthermore, it is unclear whether an agonist-induced secretory event modifies kinesin function and distribution, thus altering vesicle transport. To this end, we utilized isolated rat pancreatic acini and cultured rat pancreatic acinar cells to examine the role of Mts and kinesin in regulated secretion. Exposure of cells to cytoskeletal antagonistic drugs demonstrated that the observed movements of apically clustered zymogen granules (ZGs) are supported by Mts, but not actin. Morphological studies of Mt organization in polarized acini show that Mt plus ends extend outward from the apical membrane toward the cell center. Immunofluorescence microscopy in both cell models revealed a clear association of kinesin with apical ZGs, while quantitative immunoblot analysis of pancreatic subcellular fractions confirmed kinesin enrichment on ZG membranes. In addition, microinjection of kinesin antibodies into cultured acinar cells inhibited ZG movements. Indirect immunofluorescence staining of isolated cells and quantitative Western blotting of isolated ZGs revealed that kinesin association with granule membranes increased up to 3-fold in response to a secretory stimulus. Autoradiographic studies of 32P-labeled acini showed up to a 6-fold increase in kinesin heavy chain (KHC) phosphorylation during stimulated secretion. These studies provide the first direct evidence that Mts and kinesin support ZG movements and that physiological agonists induce a marked phosphorylation of KHC while increasing the association of kinesin with ZG membranes. These changes during agonist stimulation suggest that the participation of kinesin in zymogen secretion is regulated.

Reduced cholecystokinin receptor phosphorylation and restored signalling in protein kinase C down-regulated rat pancreatic acinar cells

Receptor phosphorylation in response to agonist stimulation is a key regulatory principle in signal transduction. Previous work has suggested the concerted action of protein kinase C (PKC) and a staurosporine-insensitive receptor kinase in homologous phosphorylation of the cholecystokinin (CCK) receptor in freshly isolated rat pancreatic acinar cells [Gates, Ulrich, Miller (1993) Am J Physiol 264:G840-G847]. The present study shows that down-regulation of PKC by prolonged (2 h) treatment with 0.1 muM 12-O-tetradecanoylphorbol-13-acetate (TPA) markedly reduced basal CCK receptor phosphorylation as well as that induced by TPA (0.1 muM) and cholecystokinin-(26-33)-peptide amide (CCK8, 0.1 muM). The phosphorylation level reached was the same with both stimulants and equalled basal phosphorylation in untreated control cells. The absence of any CCK8-stimulated phosphorylation reflecting the activity of a putative staurosporine-insensitive receptor kinase raises the intriguing possibility that a basal level of PKC-mediated receptor phosphorylation is required for the action of such a receptor kinase. Immunoblot analysis revealed that the decrease in receptor phosphorylation coincided with a marked reduction of PKC-alpha and, to a lesser extent, PKC-epsilon. In addition, TPA-induced inhibition of the increase in cytosolic free Ca2+ concentration ([Ca2+]i) evoked by the high-affinity CCK receptor agonist JMV-180 was completely reversed. The time-course of recovery closely matched that of the reduction of PKC-alpha. Finally, digital imaging microscopy of individual PKC down-regulated cells revealed a marked increase in the duration of JMV-180-evoked oscillatory changes in [Ca2+]i. Taken together, the present findings are in agreement with the idea that PKC-alpha-mediated receptor phosphorylation leads to a shortening of the duration of the [Ca2+]i oscillations and eventually to inhibition of high-affinity Ca2+ signalling through the native CCK receptor in pancreatic acinar cells.

Propofol for the long-term sedation of a critically ill patient

OBJECTIVE: To report a case in which propofol was used successfully in an intubated patient on a prolonged basis and to review the literature that discusses long-term infusions (> 7 days) of propofol. METHODS: Information was retrieved from a MEDLINE search of the English-language literature. Reports of clinical trials and case reports that compared the safety and efficacy of long-term propofol and midazolam were included in this review. Information about the study design and the efficacy and adverse effects of the drugs was collected, and the data were synthesized. RESULTS: Clinical reports indicate that a long-term infusion of propofol is comparable in safety and efficacy to a long-term infusion of midazolam. The distinct adverse-effect profile of long-term use of propofol, including hypertriglyceridemia, was evaluated and reported as significant. CONCLUSION: The limited data available suggest that long-term infusion of propofol is a practical alternative to use of standard agents for sedation of intubated patients. Adverse effects such as cardiovascular depression, respiratory depression, and hypertriglyceridemia may limit the routine use of propofol.

Angiogenesis and prostate cancer: in vivo and in vitro expression of angiogenesis factors by prostate cancer cells

OBJECTIVES

Recently, it was confirmed that angiogenesis is important in the development and spread of a variety of human cancers, including prostate cancer (PCa). Tumor neovascularization is thought to be controlled by chemical signals, known as angiogenic factors (AF). To date, little is known regarding the existence and role of AF in PCa. We previously reported on vascular endothelial growth factor (VEGF) in PCa. Currently, we compare VEGF expression with that of interleukin-8 (IL-8), another putative regulator of angiogenesis. We evaluated the expression of these two important AF in PCa and explored the role of inflammatory cytokines IL-1 and tumor necrosis factor (TNF) in their regulation.

METHODS

Ex vivo studies involved previously reported immunohistochemical analysis for VEGF and recent evaluation of IL-8 expression and distribution in archival tissue samples of PCa, benign prostatic hyperplasia (BPH), and normal prostate tissue. In vitro studies used PCa cells (DU-145) grown in culture and stimulated with cytokines thought to induce VEGF and IL-8 (ie, IL-1 alpha, IL-1 beta, TNF-alpha, and TNF-beta). After 24 hours, with or without cytokines, cell culture supernatants were analyzed by enzyme-linked immunosorbent assay or radioimmunoassay for VEGF or IL-8 levels.

RESULTS

Immunohistochemical studies of prostate tissue showed that PCa cells stained positively for VEGF and IL-8. Benign prostatic hyperplasia and normal prostate cells displayed little staining for either AF. Low levels of VEGF and IL-8 were produced by unstimulated DU-145 cells. Induction of DU-145 cells with cytokines resulted in differential stimulation whereby TNF was the predominant inducer of VEGF, whereas IL-1 was the predominant inducer of IL-8.

CONCLUSIONS

Our results indicate that significant levels of VEGF and IL-8 are present in PCa, but not BPH or normal prostate cells in vivo. In vitro studies suggest that differential regulation of AF expression occurs in PCa. Because IL-1 and TNF are present in the PCa tumor microenvironment, it is likely that differential regulation of AF also occurs in human PCa and contributes to differential tumor growth and metastasis.

1996 Comfort Symposium on Pancreatic Carcinogenesis

This article summarizes the proceedings of the 1996 Comfort Symposium on Pancreatic Carcinogenesis that took place at the Mayo Clinic in Rochester, Minnesota, September 11-13, 1996. The annual series of Comfort lectures are aimed at discussing leading theories and advanced technological developments in the area of pancreatic research. The goals of this year's symposium were to summarize epidemiologic and experimental findings in the field of pancreatic cancer research, to foster communications among scientists studying this disease, and to identify areas of research that are likely to bridge the gaps between basic science and patient care. The topics discussed included (i) current algorithms for the diagnosis of early pancreatic cancer, (ii) animal and cellular models of pancreatic carcinogenesis, (iii) mechanisms of pain in pancreatic cancer, (iv) the role of signaling cascades and transcription factors in the regulation of pancreatic cell growth and differentiation, (v) methods to study genetic alterations associated with neoplastic diseases, and (vi) recent developments in gene-targeting techniques. The lectures and discussions during the symposium successfully achieved the goals outlined above and resulted in the identification of novel areas of research that may increase our understanding of the etiology and pathogenesis, and lead to early diagnosis and treatment of pancreatic cancer.

Expression of interleukin-8 receptors on tumor cells and vascular endothelial cells in human breast cancer tissue

Recently, we demonstrated the presence of Interleukin-8 (IL-8) in human breast cancer (HBC) tissue. We hypothesize that the IL-8 receptors are present and play a role in tumor cell and vascular endothelial cell (VEC) activation (e.g. proliferation and angiogenesis).

MATERIALS AND METHODS

Immunohistochemical analysis for IL-8 receptors (IL-8RA and IL-8RB) was performed on 43 malignant and 8 benign breast tissue samples.

RESULTS

Tumor cells expressed IL-8RA and IL-8RB in all of the malignant specimens. Only 50% of the benign ductal epithelial cell (DEC) samples expressed these receptors. The majority of small vessel endothelial cells (SVEC) expressed IL-8RA and IL-8RB, while large vessel endothelial cells (LVEC) showed primarily IL-8RB expression.

CONCLUSIONS

Our results demonstrate that tumor and VEC express the IL-8 receptors and likely play a role in regulating tumor and VEC activation which controls proliferation, angiogenesis and metastasis in HBC.

Propofol for the long-term sedation of a critically ill patient

OBJECTIVE

To report a case in which propofol was used successfully in an intubated patient on a prolonged basis and to review the literature that discusses long-term infusions (> 7 days) of propofol.

METHODS

Information was retrieved from a MEDLINE search of the English-language literature. Reports of clinical trials and case reports that compared the safety and efficacy of long-term propofol and midazolam were included in this review. Information about the study design and the efficacy and adverse effects of the drugs was collected, and the data were synthesized.

RESULTS

Clinical reports indicate that a long-term infusion of propofol is comparable in safety and efficacy to a long-term infusion of midazolam. The distinct adverse-effect profile of long-term use of propofol, including hypertriglyceridemia, was evaluated and reported as significant.

CONCLUSION

The limited data available suggest that long-term infusion of propofol is a practical alternative to use of standard agents for sedation of intubated patients. Adverse effects such as cardiovascular depression, respiratory depression, and hypertriglyceridemia may limit the routine use of propofol.

Sexuality, reproduction, and family planning in women with schizophrenia

This article reviews data about how schizophrenia affects sexuality, pregnancy, the puerperium, parenting, and family planning. Women with schizophrenia have high rates of coerced sex, sexual risk behavior, and unwanted pregnancies. High rates of obstetric complications and custody loss increase morbidity for women and their offspring. Since untreated psychosis increases these problems, the risks of withholding pharmacotherapy must be weighed against the risks of prescribing medications during pregnancy. The puerperium is a time when women are especially vulnerable to exacerbations of schizophrenia. Mothers with schizophrenia may have a reduced ability to read children's cues, and they often have weak social support networks. Their children may be more difficult to raise than other children. Parenting rehabilitation can address some of these problems. Often, women with schizophrenia who are sexually active and do not wish to become pregnant do not use contraception. Incorporating family planning measures into mental health care delivery systems may reduce unwanted pregnancies.

Direct identification of a distinct site of interaction between the carboxyl-terminal residue of cholecystokinin and the type A cholecystokinin receptor using photoaffinity labeling

Mechanisms of ligand binding and activation of G protein-coupled receptors are particularly important, due to their ubiquitous expression and potential as drug targets. Molecular interactions between ligands and these receptors are best defined for small molecule ligands that bind within the transmembrane helices. Extracellular domains seem to be more important for peptide ligands, based largely on effects of receptor mutagenesis, where interference with binding or activity can reflect allosteric as well as direct effects. We now take the more direct approach of photoaffinity labeling the active site of the cholecystokinin (CCK) receptor, using a photolabile analogue of CCK having a blocked amino terminus. This probe, 125I-desaminotyrosyl-Gly-[Nle28,31, pNO2-Phe33]CCK-(26-33), binds specifically, saturably, and with high affinity (Ki = 3.3 nM) and has full agonist activity. This makes likely its being sited in a natural position within the receptor. As substrate, we used CHO-CCK receptor cells overexpressing functional recombinant rat type A CCK receptor. Covalent labeling of the appropriate Mr = 85,000-95,000 plasma membrane glycoprotein with core of Mr = 42,000 was established by SDS-polyacrylamide gel electrophoresis and autoradiography. A single domain adjacent to transmembrane 1 was labeled, as established by cyanogen bromide cleavage and separation by gel and/or high pressure liquid chromatography. The site of interaction was further defined by additional proteolysis with trypsin, with purification of the labeled fragment, followed by manual Edman degradation and radiochemical sequencing. This demonstrated that Trp39 was specifically labeled and likely resides proximate to the carboxyl-terminal pNO2-Phe33 residue of the probe. A model of this ligand-bound receptor has been constructed and will be used to plan future experiments to refine our understanding of this interaction.

Differences in partial agonist action at cholecystokinin receptors of mouse and rat are dependent on parameters extrinsic to receptor structure: molecular cloning, expression and functional characterization of the mouse type A cholecystokinin receptor

The mouse cholecystokinin (CCK) receptor is functionally distinct from the extensively studied rat receptor on the basis of differences in binding and biological activity of phenethyl ester analogs of CCK. These are partial agonists at the rat receptor and full agonists at the mouse pancreatic receptor. To explore this, we cloned the cDNA for the mouse type A CCK receptor, established a receptor-bearing Chinese hamster ovary (CHO) cell line and characterized its binding and biological characteristics. Despite 25 differences in amino acid sequence from the rat receptor, including a seven-amino acid insertion in the third intracellular loop, mouse and rat receptors were functionally indistinguishable when expressed in CHO cells. Of note, in the mouse pancreatic cell environment, a stable analog of guanosine triphosphate significantly inhibited binding of CCK-OPE, whereas it had no effect on binding to the same receptor on the CHO-CCKM cell line or to the rat receptor in either environment of the acinar cell. This likely reflects a difference in coupling of the mouse receptor to its G protein in the natural environment of the acinar cell. This may relate to differences extrinsic to the receptor, in the stoichiometry or character of G proteins or in the composition or organization of the lipid environment of the mouse acinar cell membrane. Although this may require complementation of the unique sequence of the mouse receptor, that structure alone is insufficient to explain this phenomenon. Receptor microenvironment makes an important, yet often ignored, contribution to receptor function.

Hydrophobic peptide mapping of clinically relevant heptathelical membrane proteins by capillary electrophoresis

The structural investigation of G protein-coupled receptors has been hindered by the lack of techniques to effectively resolve the hydrophobic peptides obtained by chemical or proteolytic cleavage, as well as the minute amounts of protein typically isolated. We have developed a capillary electrophoresis method for efficient separation of hydrophobic peptides using a cyanogen bromide digest of bacteriorhodopsin as a model for these clinically important membrane proteins. This procedure includes (i) solubilization of the protein digest in acetic acid; and (ii) electrophoresis using an acetic acid-based buffer system augmented by acetonitrile and hexane sulfonic acid, in a Polybrene-coated fused silica capillary. The potential for detection sensitivity to be increased at least 100-fold by use of on-line solid-phase extraction on C18-silica is shown. This approach is potentially useful for peptide fingerprinting of sparse and extremely hydrophobic membrane receptors.

Congenital ganglioglioma: report of a case with an unusual imaging appearance

A newborn presented with a cerebral ganglioglioma. This is a rare diagnosis in a neonate. The imaging appearance (hyperdense on CT, hyperintense on T1-weighted and hypointense on T2-weighted MRI) is very unusual for this type of tumor.

Postconcussion syndrome occurs in children

The consensus of evidence published since 1924 suggests that parents report attention deficits, hyperactivity, or conduct disorder after pediatric head injury rather than postconcussion syndrome. In this study, the symptoms reported by children after mild (n = 38) and moderate-severe (n = 27) head trauma were compared to those reported after orthopedic injury (n = 47) and to adults matched for injury severity and chronicity by using a structured interview based on diagnostic criteria for postconcussion syndrome. Pediatric head trauma caused significantly more subjective symptoms after 6 weeks than orthopedic injury. These symptoms were related to head injury severity and the child's anxiety level. When assessed in a similar manner, children report postconcussion syndrome similar to that seen in adults.

Neuroanatomical distribution of vasotocin in a urodele amphibian (Taricha granulosa) revealed by immunohistochemical and in situ hybridization techniques

Immunohistochemical and in situ hybridization techniques were used to investigate the neuroanatomical distribution of arginine vasotocin-like systems in the roughskin newt (Taricha granulosa). Vasotocin-like-immunoreactive neuronal cell bodies were identified that, based on topographical position, most likely, are homologous to groups of vasopressin-immunoreactive neuronal cell bodies described in mammals, including those in the bed nucleus of the stria terminalis, medial amygdala, basal septal region, magnocellular basal forebrain-including the horizontal limb of the diagonal band of Broca, paraventricular and supraoptic nuclei, suprachiasmatic nucleus, and dorsomedial hypothalamic nucleus. Several additional vasotocin-like-immunoreactive cell groups were observed in the forebrain and brainstem regions; these observations are compared with previous studies of vasotocin- and vasopressin-like systems in vertebrates. Arginine vasotocin-like-immunoreactive fibers and presumed terminals also were widely distributed with high densities in the basal limbic forebrain, the ventral preoptic and hypothalamic regions, and the brainstem ventromedial tegmentum. Based on in situ hybridization studies with synthetic oligonucleotide probes for vasotocin and the related neuropeptide mesotocin, as well as double-labeling studies with combined immunohistochemistry and in situ hybridization, we conclude that the vasotocin immunohistochemical procedures used identify vasotocin-like, but not mesotocin-like, elements in the brain of T. granulosa. The distribution of arginine vasotocin-like systems in T. granulosa is greater than the distribution previously reported for any other single vertebrate species; however, it is consistent with an emerging pattern of distribution of vasotocin- and vasopressin-like peptides in vertebrates. Complexity in the vasotocinergic system adds further support to the conclusion that this peptide regulates multiple neurophysiological and neuroendocrinological functions.

Postconcussion syndrome occurs in children

The consensus of evidence published since 1924 suggests that parents report attention deficits, hyperactivity, or conduct disorder after pediatric head injury rather than postconcussion syndrome. In this study, the symptoms reported by children after mild (n = 38) and moderate-severe (n = 27) head trauma were compared to those reported after orthopedic injury (n = 47) and to adults matched for injury severity and chronicity by using a structured interview based on diagnostic criteria for postconcussion syndrome. Pediatric head trauma caused significantly more subjective symptoms after 6 weeks than orthopedic injury. These symptoms were related to head injury severity and the child's anxiety level. When assessed in a similar manner, children report postconcussion syndrome similar to that seen in adults.

Cholecystokinin-induced desensitization, receptor phosphorylation, and internalization in the CHP212 neuroblastoma cell line

Agonist stimulation of cells often results in desensitization of the response, to protect the cell from overstimulation. We have previously shown that the type A cholecystokinin (CCK) receptor on the pancreatic acinar cell and on the model CHO-CCKR cell line undergoes desensitization in response to CCK, with receptor phosphorylation and internalization playing key roles. Although these mechanisms contribute in a cell-specific manner, no analogous information exists for the CCK receptor expressed on neuronal cells, where in vivo data demonstrate a particularly sensitive response to CCK. The present study was designed to explore CCK receptor desensitization in the CHP212 neuroblastoma cell line, focusing on inositol 1,4,5-trisphosphate (IP3) responses to CCK and on recognized molecular and cellular mechanisms of desensitization. CCK promptly stimulated IP3 responses in these cells, with hormonal responsiveness rapidly and completely desensitized. Both receptor phosphorylation and internalization were observed to occur, with the former occurring most rapidly and likely being responsible for the earliest desensitization observed. Although the time course of receptor phosphorylation and dephosphorylation, and the groups of kinases involved in the neuroblastoma cell line, were most similar to those in the pancreatic cell, the movement of the agonist-bound receptor in these cells was quite different from that in the pancreatic cell and most similar to that in the CHO-CCKR cell line. This hybrid response supports the cell-specific nature of CCK receptor regulation and provides an important system to explore the molecular determinants of these processes.

Vascular endothelial growth factor (VEGF) expression in human prostate cancer: in situ and in vitro expression of VEGF by human prostate cancer cells

PURPOSE

A growing body of literature supports the role of angiogenesis in the development and spread of a variety of human cancers including prostate cancer (Pca). Angiogenesis is controlled by chemical signals known as angiogenic factors (AF) however, little is known about angiogenesis factors in prostate cancer. We evaluated the in situ and in vitro expression of vascular endothelial growth factor (VEGF), a potent angiogenic factor, in archival prostate cancer specimens and prostate cancer cell cultures during unstimulated and cytokine stimulated conditions.

METHODS

Ex-vivo studies involved immunohistochemical analysis for VEGF expression and distribution in 25 archival specimens including, prostate cancer, benign prostatic hyperplasia (BPH) and normal prostate tissue. In-vitro studies utilized prostate cancer cells (DU-145) grown in culture and stimulated with cytokines thought to induce VEGF (i.e. IL-1 alpha, IL-1 beta, TNF-alpha and TNF-beta). Cell culture supernatants were analyzed by ELISA for VEGF levels.

RESULTS

Immunohistochemical studies demonstrated that in 20 of 25 specimens prostate cancers cells stained positively for VEGF. BPH and normal prostate cells displayed little staining for VEGF. DU-145 prostate cancer cells produced low levels of VEGF in unstimulated conditions. Induction of DU-145 cells with cytokines resulted in differential stimulation whereby TNF was a potent inducer of VEGF, and IL-1 produced lesser but statistically significant increases in VEGF expression.

CONCLUSIONS

Our immunohistochemical results indicate that significant levels of VEGF are present in prostate cancer, but not in BPH or normal prostate cells in-vivo. In-vitro studies suggest that differential regulation of angiogenesis factor expression by IL-1 and TNF occurs in prostate cancer. Identifying the angiogenesis factors involved in prostate cancer growth and understanding their regulation will lead to the development of anti-angiogenic strategies useful for diagnostic studies and therapeutic interventions.

Quantitative dynamic multicompartmental analysis of cholecystokinin receptor movement in a living cell using dual fluorophores and reconstruction of confocal images

Receptor regulation is a key component of the phenomenon of desensitization in response to agonist stimulation which protects cells from overstimulation. Receptor internalization is one part of this response, often quantified by the portion of saturable ligand binding which becomes resistant to acidic washes. It is now clear that this can include receptor in multiple distinct cellular compartments. We have developed a morphological technique involving dual fluorescent probes to delineate the plasmalemma and the ligand-occupied receptor using confocal microscopy, with analysis involving three-dimensional reconstruction and quantitation of receptor movement through each compartment. When a radioiodinated cholecystokinin (CCK) analogue occupied its receptor on the CHO-CCKR cell line, it became progressively more resistant to dissociation with acidic medium. Quantitation of receptor internalization in these cells over time using this dynamic morphological technique correlated with the acid-resistant receptor fraction, and provided the additional information of the cellular compartments traversed. This technique will have multiple applications to explore the cell-specific handling of this and other ligand-occupied receptors.

Cellular handling of unoccupied and agonist-stimulated cholecystokinin receptor determined by immunolocalization

Cellular handling of receptor molecules is an important mechanism for the regulation of appropriately sensitive hormone-stimulated signaling. Until now, our understanding of the cellular handling of the cholecystokinin (CCK) receptor has been largely limited to following a tagged ligand through the cell. In the present work, we report the application of unique CCK receptor antisera directed toward intracellular domains, which permitted the immunolocalization of this molecule independently of its occupation with ligand. The CCK receptor antisera were also useful in Western blotting and immunoprecipitation of this receptor. Unstimulated CCK receptors remained on the surface of both recombinant stable rat CCK-A receptor-bearing Chinese hamster ovary cell line (CHO-CCKR) cells and native rat pancreatic acinar cells and did not constitutively internalize. Agonist stimulation of the CHO-CCKR cells resulted in the prompt internalization of a subset of surface receptors, representing those that were occupied with ligand. Unoccupied receptors remained on the surface, uninfluenced by the stimulated signaling pathways. Consistent with this, CCK receptor phosphorylation induced by 12-O-tetradecanoylphorbol-13-acetate treatment did not stimulate receptor internalization. After internalization, we observed substantial receptor recycling to the plasma membrane. These insights provide the first evidence that CCK receptor internalization occurs as a direct result of an induced conformational change and presumed bimolecular interaction, rather than as an effect of a signaling event.

Antagonist-stimulated internalization of the G protein-coupled cholecystokinin receptor

Receptor-mediated endocytosis has been observed after agonist occupation of several G protein-coupled receptors, which contributes to the desensitization response to agonist stimulation; however, the cellular signals required to initiate this process are unclear. In this study, we developed and characterized a new antagonist analogue of cholecystokinin (D-Tyr-Gly-[(Nle28,31,D-Trp30)cholecystokinin-26-32]-phen eth yl ester) that can be tagged with a fluorescent rhodamine and radioiodinated. This has permitted us to demonstrate that antagonist occupation of the cholecystokinin receptor also results in receptor internalization, which dissociates this response from second messenger signaling activities and receptor phosphorylation. Immunolocalization of this receptor after occupation with an established nonpeptidyl antagonist confirmed this phenomenon. Antagonist-induced receptor internalization probably results from stabilization of the receptor in a conformation that exposes a domain critical to directing it into the clathrin-dependent endocytic pathway. This work provides evidence for a new and independent mechanism for receptor internalization, provides a mechanism for the rarely observed phenomenon of antagonist-induced desensitization, and raises important issues regarding the approach to establish optimal treatment regimens for antagonist drugs.

Roles of cholecystokinin receptor phosphorylation in agonist-stimulated desensitization of pancreatic acinar cells and receptor-bearing Chinese hamster ovary cholecystokinin receptor cells

Receptor phosphorylation has been implicated in desensitization responses to some agonist ligands, in which receptors may become uncoupled from G proteins and move into cellular compartments inaccessible to hydrophilic ligands. Understanding of the linkage between these processes, however, has come largely from recombinant receptor-bearing cell systems with consensus sites of kinase action mutagenized. We recently established methodology permitting direct assessment of sites of phosphorylation of the cholecystokinin receptor (CCKR) in its native milieu in the pancreatic acinar cell and in a Chinese hamster ovary (CHO)-CCKR cell line (1, 2). Although CCK binding leads to phosphorylation of serine residues within the third intracellular loop of the receptor in both cell types, there are clear differences in the time course of phosphorylation, in the balance of action of kinases and a receptor phosphatase, and in a few of the distinct sites phosphorylated. In this work, we have directly assessed the inositol 1,4,5-triphosphate responses to CCK and desensitization of these responses in both cells. CHO cell lines expressing receptor mutants with protein kinase C consensus sites modified were also studied. CCK-stimulated inositol 1,4,5-triphosphate responses in both cells expressing wild-type receptors were rapidly and completely desensitized, associated with the onset of receptor phosphorylation. However, despite maintenance of the phosphorylated state of the receptor in the CHO-CCKR cell and its dephosphorylation returning the receptor to its basal state in the acinar cell, desensitization continued to be present in both. Mutagenesis of Ser260 and Ser264 to alanines individually reduced receptor phosphorylation by approximately 50%, whereas the dual mutant completely eliminated agonist-stimulated phosphorylation. Because other sites of phosphorylation were still intact in this construct, this raises the possibility of hierarchical phosphorylation with these two sites key in making other sites accessible to kinases. Constructs modifying Ser264 delayed the onset of desensitization, whereas all constructs proceeded to achieve complete desensitization by 10 min. Receptor internalization occurred independent of its phosphorylation state in the CHO cell lines, explaining the desensitization observed. In the acinar cell in which the receptor remains on the cell surface after agonist occupation, we postulate that receptor insulation achieves similar uncoupling from G protein association as is achieved by receptor phosphorylation early after agonist occupation.