Non-ionotropic voltage-gated calcium channel signaling

Voltage-gated calcium channels (VGCCs) are the major conduits for calcium ions (Ca2+) within excitable cells. Recent studies have highlighted the non-ionotropic functionality of VGCCs, revealing their capacity to activate intracellular pathways independently of ion flow. This non-ionotropic signaling mode plays a pivotal role in excitation-coupling processes, including gene transcription through excitation-transcription (ET), synaptic transmission via excitation-secretion (ES), and cardiac contraction through excitation-contraction (EC). However, it is noteworthy that these excitation-coupling processes require extracellular calcium (Ca2+) and Ca2+ occupancy of the channel ion pore. Analogous to the "non-canonical" characterization of the non-ionotropic signaling exhibited by the N-methyl-D-aspartate receptor (NMDA), which requires extracellular Ca2+ without the influx of ions, VGCC activation requires depolarization-triggered conformational change(s) concomitant with Ca2+ binding to the open channel. Here, we discuss the contributions of VGCCs to ES, ET, and EC coupling as Ca2+ binding macromolecules that transduces external stimuli to intracellular input prior to elevating intracellular Ca2+. We emphasize the recognition of calcium ion occupancy within the open ion-pore and its contribution to the excitation coupling processes that precede the influx of calcium. The non-ionotropic activation of VGCCs, triggered by the upstroke of an action potential, provides a conceptual framework to elucidate the mechanistic aspects underlying the microseconds nature of synaptic transmission, cardiac contractility, and the rapid induction of first-wave genes.

Identification of cells of leukemic stem cell origin with non-canonical regenerative properties

Despite most acute myeloid leukemia (AML) patients entering remission following chemotherapy, outcomes remain poor due to surviving leukemic cells that contribute to relapse. The nature of these enduring cells is poorly understood. Here, through temporal single-cell transcriptomic characterization of AML hierarchical regeneration in response to chemotherapy, we reveal a cell population: AML regeneration enriched cells (RECs). RECs are defined by CD74/CD68 expression, and although derived from leukemic stem cells (LSCs), are devoid of stem/progenitor capacity. Based on REC in situ proximity to CD34-expressing cells identified using spatial transcriptomics on AML patient bone marrow samples, RECs demonstrate the ability to augment or reduce leukemic regeneration in vivo based on transfusion or depletion, respectively. Furthermore, RECs are prognostic for patient survival as well as predictive of treatment failure in AML cohorts. Our study reveals RECs as a previously unknown functional catalyst of LSC-driven regeneration contributing to the non-canonical framework of AML regeneration.

Preclinical characterization and clinical trial of CFI-400945, a polo-like kinase 4 inhibitor, in patients with relapsed/refractory acute myeloid leukemia and higher-risk myelodysplastic neoplasms

CFI-400945 is a selective oral polo-like kinase 4 (PLK4) inhibitor that regulates centriole duplication. PLK4 is aberrantly expressed in patients with acute myeloid leukemia (AML). Preclinical studies indicate that CFI-400945 has potent in vivo efficacy in hematological malignancies and xenograft models, with activity in cells harboring TP53 mutations. In this phase 1 study in very high-risk patients with relapsed/refractory AML and myelodysplastic syndrome (MDS) (NCT03187288), 13 patients were treated with CFI-400945 continuously in dose escalation from 64 mg/day to 128 mg/day. Three of the 9 efficacy evaluable AML patients achieved complete remission (CR). Two of 4 AML patients (50%) with TP53 mutations and complex monosomal karyotype achieved a CR with 1 patient proceeding to allogenic stem cell transplant. A third patient with TP53 mutated AML had a significant reduction in marrow blasts by > 50% with an improvement in neutrophil and platelet counts. Responses were observed after 1 cycle of therapy. Dose-limiting toxicity was enteritis/colitis. A monotherapy and combination therapy study with a newer crystal form of CFI-400945 in patients with AML, MDS and chronic myelomonocytic leukemia (CMML) is ongoing (NCT04730258).

Leukemic progenitor compartment serves as a prognostic measure of cancer stemness in patients with acute myeloid leukemia

We systematically investigate functional and molecular measures of stemness in patients with acute myeloid leukemia (AML) using a cohort of 121 individuals. We confirm that the presence of leukemic stem cells (LSCs) detected through in vivo xenograft transplantation is associated with poor survival. However, the measurement of leukemic progenitor cells (LPCs) through in vitro colony-forming assays provides an even stronger predictor of overall and event-free survival. LPCs not only capture patient-specific mutations but also retain serial re-plating ability, demonstrating their biological relevance. Notably, LPC content represents an independent prognostic factor in multivariate analyses including clinical guidelines of risk stratification. Our findings suggest that LPCs provide a robust functional measure of AML, enabling quantitative and rapid assessment of a wide range of patients. This highlights the potential of LPCs as a valuable prognostic factor in AML management.

Elevated basal transcription can underlie timothy channel association with autism related disorders

Timothy syndrome (TS) is a neurodevelopmental disorder caused by mutations in the pore-forming subunit α₁1.2 of the L-type voltage-gated Ca²⁺-channel Cav1.2, at positions G406R or G402S. Although both mutations cause cardiac arrhythmias, only Cav1.2^G406R is associated with the autism-spectrum-disorder (ASD). We show that transcriptional activation by Cav1.2^G406R and Cav1.2^G402S is driven by membrane depolarization through the Ras/ERK/CREB pathway in a process called excitation-transcription (ET) coupling, as previously shown for wt Cav1.2. This process requires the presence of the intracellular β-subunit of the channel. We found that only the autism-associated mutant Cav1.2^G406R, as opposed to the non-autistic mutated channel Cav1.2^G402S, exhibits a depolarization-independent CREB phosphorylation, and spontaneous transcription of cFos and MeCP2. A leftward voltage-shift typical of Cav1.2^G406R activation, increases channel opening at subthreshold potentials, resulting in an enhanced channel activity, as opposed to a rightward shift in Cav1.2^G402S. We suggest that the enhanced spontaneous Cav1.2^G406R activity accounts for the increase in basal transcriptional activation. This uncontroled transcriptional activation may result in the manifestation of long-term dysregulations such as autism. Thus, gating changes provide a mechanistic framework for understanding the molecular events underlying the autistic phenomena caused by the G406R Timothy mutation. They might clarify whether a constitutive transcriptional activation accompanies other VGCC that exhibit a leftward voltage-shift of activation and are also associated with long-term cognitive disorders.

Intra-membrane signaling between the voltage-gated Ca2+-channel and cysteine residues of syntaxin 1A coordinates synchronous release

The interaction of syntaxin 1A (Sx1A) with voltage-gated calcium channels (VGCC) is required for depolarization-evoked release. However, it is unclear how the signal is transferred from the channel to the exocytotic machinery and whether assembly of Sx1A and the calcium channel is conformationally linked to triggering synchronous release. Here we demonstrate that depolarization-evoked catecholamine release was decreased in chromaffin cells infected with semliki forest viral vectors encoding Sx1A mutants, Sx1A^C271V, or Sx1A^C272V, or by direct oxidation of these Sx1A transmembrane (TM) cysteine residues. Mutating or oxidizing these highly conserved Sx1A Cys271 and Cys272 equally disrupted the Sx1A interaction with the channel. The results highlight the functional link between the VGCC and the exocytotic machinery, and attribute the redox sensitivity of the release process to the Sx1A TM C271 and C272. This unique intra-membrane signal-transduction pathway enables fast signaling, and triggers synchronous release by conformational-coupling of the channel with Sx1A.

Thioredoxin-mimetic peptides (TXM) reverse auranofin induced apoptosis and restore insulin secretion in insulinoma cells

The thioredoxin reductase/thioredoxin system (TrxR/Trx1) plays a major role in protecting cells from oxidative stress. Disruption of the TrxR-Trx1 system keeps Trx1 in the oxidized state leading to cell death through activation of the ASK1-Trx1 apoptotic pathway. The potential mechanism and ability of tri- and tetra-oligopeptides derived from the canonical -CxxC- motif of the Trx1-active site to mimic and enhance Trx1 cellular activity was examined. The Trx mimetics peptides (TXM) protected insulinoma INS 832/13 cells from oxidative stress induced by selectively inhibiting TrxR with auranofin (AuF). TXM reversed the AuF-effects preventing apoptosis, and increasing cell-viability. The TXM peptides were effective in inhibiting AuF-induced MAPK, JNK and p38(MAPK) phosphorylation, in correlation with preventing caspase-3 cleavage and thereby PARP-1 dissociation. The ability to form a disulfide-bridge-like conformation was estimated from molecular dynamics simulations. The TXM peptides restored insulin secretion and displayed Trx1 denitrosylase activity. Their potency was 10-100-fold higher than redox reagents like NAC, AD4, or ascorbic acid. Unable to reverse ERK1/2 phosphorylation, TXM-CB3 (NAc-Cys-Pro-Cys amide) appeared to function in part, through inhibiting ASK1-Trx dissociation. These highly effective anti-apoptotic effects of Trx1 mimetic peptides exhibited in INS 832/13 cells could become valuable in treating adverse oxidative-stress related disorders such as diabetes.

Adjuvant Chemotherapy for Breast Cancer in a Patient with Primary Autoimmune Neutropenia

We report an extremely rare and complex case of a 44-year-old woman diagnosed with an early stage triple negative breast cancer in the setting of primary autoimmune neutropenia with a pre-existing severe neutropenia. This case-report demonstrates that adjuvant chemotherapy for breast cancer can be administered in a patient with severe neutropenia. The management is however complicated and requires careful monitoring of side-effects related to both chemotherapy and treatment of autoimmune neutropenia. The role of chemotherapy in the treatment of triple negative breast cancer, the approach to autoimmune neutropenia and potential interactions are reviewed. To our knowledge, this is the first case reporting on the use of chemotherapy in a patient with severe pre-existing primary autoimmune neutropenia.

Calcineurin Controls Voltage-Dependent-Inactivation (VDI) of the Normal and Timothy Cardiac Channels

Ca²⁺-entry in the heart is tightly controlled by Cav1.2 inactivation, which involves Ca²⁺-dependent inactivation (CDI) and voltage-dependent inactivation (VDI) components. Timothy syndrome, a subtype-form of congenital long-QT syndrome, results from a nearly complete elimination of VDI by the G406R mutation in the α₁1.2 subunit of Cav1.2. Here, we show that a single (A1929P) or a double mutation (H1926A-H1927A) within the CaN-binding site at the human C-terminal tail of α₁1.2, accelerate the inactivation rate and enhances VDI of both wt and Timothy channels. These results identify the CaN-binding site as the long-sought VDI-regulatory motif of the cardiac channel. The substantial increase in VDI and the accelerated inactivation caused by the selective inhibitors of CaN, cyclosporine A and FK-506, which act at the same CaN-binding site, further support this conclusion. A reversal of enhanced-sympathetic tone by VDI-enhancing CaN inhibitors could be beneficial for improving Timothy syndrome complications such as long-QT and autism.

A review of pneumatosis intestinalis in the setting of systemic cancer treatments, including tyrosine kinase inhibitors

PURPOSE

Pneumatosis intestinalis is a radiologic diagnosis that manifests in a variety of clinical settings. We report 4 cases of pneumatosis intestinalis in patients undergoing cancer treatments that included cytotoxic agents and/or tyrosine kinase inhibitors. These reports aim to provide insight into the clinical interpretation and pathogenesis of pneumatosis intestinalis in the setting of cancer treatments and demonstrate a potential association with tyrosine kinase inhibitors.

METHODS

Radiologists responsible for the interpretation of adult imaging at our tertiary care centre were surveyed to identify cases of pneumatosis intestinalis arising in the midst of cancer treatment. The case histories were reviewed by physicians with expertise in cancer treatment.

RESULTS

Four cases of chemotherapy-related pneumatosis intestinalis were identified. The diagnosis was made in 1 patient during investigations undertaken for non-life-threatening abdominal symptoms and incidentally in 2 patients by abdominal imaging used to measure chemotherapy response. A fourth patient presented in a life-threatening manner, and abdominal imaging was symptom guided. Interestingly, 3 of the 4 patients were receiving treatments that included a tyrosine kinase inhibitor, and this agent was the only identifiable potential etiology in 1 patient.

CONCLUSIONS

The significance of pneumatosis intestinalis arising during cancer treatments is difficult to interpret because of the complex nature of the diseases and the treatments that often include combinations of cytotoxic agents and/or novel therapies. These reports demonstrate the importance of classifying this radiologic finding according clinical severity rather than etiology and underscore the need for continued observation for unexplained adverse effects when using novel therapies.

Alleviation of oxidative stress by potent and selective thioredoxin-mimetic peptides

One of the major enzymatic cell defenses providing protection from oxidative injury is the TrxR-Trx system. It consists of NADPH and thioredoxin reductase (TrxR), which maintain thioredoxin (Trx) in a reduced state. Perturbing the TrxR-Trx system with the selective TrxR inhibitor auranofin (AuF; 2,3,4,6-tetra-O-acetyl-1-thio-β-D-glucopyranosato-S-(triethylphosphine) gold) induces oxidative stress by keeping Trx in its oxidized state. We have prepared a family of tri- and tetra-oligopeptides derived from the canonical CxxC motif of the Trx active site and a modified CxC motif. These Trx-mimetic compounds are N- and C-terminal-blocked peptides that consist of two cysteine residues that flank the two-amino-acid CxxC motif (CB4 and CB6) or the single-amino-acid CxC motif (CB3). Catecholamine (CA) secretion in bovine chromaffin cells, which is a highly redox sensitive process, is abolished by AuF. The Trx-mimetic peptides effectively restore CA secretion, as monitored by amperometry in single cells. They also prevent the AuF-induced phosphorylation of p38 mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase. In PC12 cells, the alleviation of AuF-induced ERK1/2-MAPK phosphorylation by Trx-like peptides parallels their effect of restoring CA secretion. CB3, CB4, and CB6 act intracellularly and are significantly more potent than the traditional antioxidants NAC, GSH, DTT, AD4 (NAC-amide), and ascorbic acid. Taken together, the CxxC and CxC peptides represent a new family of potent and selective redox compounds that could serve as potential candidates for prevention and treatment of oxidative-stress-related disorders.

The L-type voltage-gated Ca2+ channel is the Ca2+ sensor protein of stimulus-secretion coupling in pancreatic beta cells

L-type voltage-gated Ca2+ channels (Cav1.2) mediate a major part of insulin secretion from pancreatic beta-cells. Cav1.2, like other voltage-gated Ca2+ channels, is functionally and physically coupled to synaptic proteins. The tight temporal coupling between channel activation and secretion leads to the prediction that rearrangements within the channel can be directly transmitted to the synaptic proteins, subsequently triggering release. La3+, which binds to the polyglutamate motif (EEEE) comprising the selectivity filter, is excluded from entry into the cells and has been previously shown to support depolarization-evoked catecholamine release from chromaffin and PC12 cells. Hence, voltage-dependent trigger of release relies on Ca2+ ions bound at the EEEE motif and not on cytosolic Ca2+ elevation. We show that glucose-induced insulin release in rat pancreatic islets and ATP release in INS-1E cells are supported by La3+ in nominally Ca2+-free solution. The release is inhibited by nifedipine. Fura 2 imaging of dispersed islet cells exposed to high glucose and La3+ in Ca2+-free solution detected no change in fluorescence; thus, La3+ is excluded from entry, and Ca2+ is not significantly released from intracellular stores. La3+ by interacting extracellularlly with the EEEE motif is sufficient to support glucose-induced insulin secretion. Voltage-driven conformational changes that engage the ion/EEEE interface are relayed to the exocytotic machinery prior to ion influx, allowing for a fast and tightly regulated process of release. These results confirm that the Ca2+ channel is a constituent of the exocytotic complex [Wiser et al. (1999) PNAS 96, 248-253] and the putative Ca2+-sensor protein of release.

Ion interaction at the pore of Lc-type Ca2+ channel is sufficient to mediate depolarization-induced exocytosis

The coupling of voltage-gated Ca2+ channel (VGCC) to exocytotic proteins suggests a regulatory function for the channel in depolarization-evoked exocytosis. To explore this possibility we have examined catecholamine secretion in PC12 and chromaffin cells. We found that replacing Ca2+ with La3+ or other lanthanide ions supported exocytosis in divalent ion-free solution. Cd2+, nifedipine, or verapamil inhibited depolarization-evoked secretion in La3+, indicating specific binding of La3+ at the pore of L-type VGCC, probably at the poly-glutamate (EEEE) locus. Lanthanide efficacy was stringently dependent on ionic radius with La3+>Ce3+>Pr3+, consistent with a size-selective binding interface of trivalent cations at the channel pore. La3+ inward currents were not detected and the highly sensitive La3+/fura-2 imaging assay (approximately 1 pm) detected no La3+ entry, cytosolic La3+ build-up, or alterations in cytosolic Ca2. These results provide strong evidence that occupancy of the pore of the channel by an impermeable cation leads to a conformational change that is transmitted to the exocytotic machinery upstream of intracellular cation build-up (intracellular Ca2+ concentration). Our model allows for a tight temporal and spatial coupling between the excitatory stimulation event and vesicle fusion. It challenges the conventional view that intracellular Ca2+ ion build-up via VGCC permeation is required to trigger secretion and establishes the VGCC as a plausible Ca2+ sensor protein in the process of neuroendocrine secretion.

Psychological factors influencing results of cholecystectomy

BACKGROUND

Cholecystectomy is a surgical gold-standard procedure for gallbladder diseases, among which gallstones are the most frequent. Despite the introduction of minimally invasive surgery and broad access to ultrasound examination there is a group of patients in whom the surgery ailments persist. Those vague ailments can be perceived from a psychological point of view as somatization or even somatoform disorders.

METHODS

The aim of the study, designed as a case-control study, was to evaluate psychological characteristics that may accompany the incidence of so-called post-cholecystectomy pain syndrome (PCPS). The study focused on 367 patients treated for gallstones in the Dept. of General, Gastroenterological and Endocrinological Surgery, Medical University of Gdańsk, Poland. At about a year after the operation, the patients received a questionnaire that included a structured interview and psychological assessment of social support and rumination. Those who revealed symptoms of PCPS were invited to the department for further medical and psychological evaluations. Psychosocial scores of PCPS and non-PCPS patients were compared.

RESULTS

The PCPS patients did not present any dysfunction at the physical examination or in gastroduodenoscopy or sonography. However, they differed from the remaining. asymptomatic group in terms of lacking social support, as well as increased rumination.

CONCLUSION

It is concluded that psychological variables may play an important role in the onset of subjective symptoms in at least a subgroup of the PCPS patients as a form of somatization. Psychological supportive and explanatory activities (cognitive and behavioural approach) may provide sufficient help.

Fast exocytosis with few Ca(2+) channels in insulin-secreting mouse pancreatic B cells

The association of L-type Ca(2+) channels to the secretory granules and its functional significance to secretion was investigated in mouse pancreatic B cells. Nonstationary fluctuation analysis showed that the B cell is equipped with <500 alpha1(C) L-type Ca(2+) channels, corresponding to a Ca(2+) channel density of 0.9 channels per microm(2). Analysis of the kinetics of exocytosis during voltage-clamp depolarizations revealed an early component that reached a peak rate of 1.1 pFs(-1) (approximately 650 granules/s) 25 ms after onset of the pulse and is completed within approximately 100 ms. This component represents a subset of approximately 60 granules situated in the immediate vicinity of the L-type Ca(2+) channels, corresponding to approximately 10% of the readily releasable pool of granules. Experiments involving photorelease of caged Ca(2+) revealed that the rate of exocytosis was half-maximal at a cytoplasmic Ca(2+) concentration of 17 microM, and concentrations >25 microM are required to attain the rate of exocytosis observed during voltage-clamp depolarizations. The rapid component of exocytosis was not affected by inclusion of millimolar concentrations of the Ca(2+) buffer EGTA but abolished by addition of exogenous L(C753-893), the 140 amino acids of the cytoplasmic loop connecting the 2(nd) and 3(rd) transmembrane region of the alpha1(C) L-type Ca(2+) channel, which has been proposed to tether the Ca(2+) channels to the secretory granules. In keeping with the idea that secretion is determined by Ca(2+) influx through individual Ca(2+) channels, exocytosis triggered by brief (15 ms) depolarizations was enhanced 2.5-fold by the Ca(2+) channel agonist BayK8644 and 3.5-fold by elevating extracellular Ca(2+) from 2.6 to 10 mM. Recordings of single Ca(2+) channel activity revealed that patches predominantly contained no channels or many active channels. We propose that several Ca(2+) channels associate with a single granule thus forming a functional unit. This arrangement is important in a cell with few Ca(2+) channels as it ensures maximum usage of the Ca(2+) entering the cell while minimizing the influence of stochastic variations of the Ca(2+) channel activity.

The voltage-gated Ca2+ channel is the Ca2+ sensor of fast neurotransmitter release

Previously it demonstrated that in the absence of Ca2+ entry, evoked secretion occurs neither by membrane depolarization, induction of [Ca2+]i rise, nor by both combined (Ashery, U., Weiss, C., Sela, D., Spira, M. E., and Atlas, D. (1993). Receptors Channels 1:217-220.). These studies designate Ca2+ entry as opposed to [Ca2+]i rise, essential for exocytosis. It led us to propose that the channel acts as the Ca+ sensor and modulates secretion through a physical and functional contact with the synaptic proteins. This view was supported by protein-protein interactions reconstituted in the Xenopus oocytes expression system and release experiments in pancreatic cells (Barg, S., Ma, X., Elliasson, L., Galvanovskis, J., Gopel, S. O., Obermuller, S., Platzer, J., Renstrom, E., Trus, M., Atlas, D., Streissnig, G., and Rorsman, P. (2001). Biophys. J; Wiser, O., Bennett, M. K., and Atlas, D. (1996). EMBO J 15:4100-4110; Wiser, O., Trus, M.. Hernandez, A., Renström, E., Barg, S., Rorsman. P., and Atlas, D. (1999). Proc. Natl. Acad. Sci. U.S.A. 96:248-253). The kinetics of Ca(v)1.2 (Lc-type) and Ca(v)2.2 (N-type) Ca2+ channels were modified in oocytes injected with cRNA encoding syntaxin 1A and SNAP-25. Conserved cysteines (Cys271, Cys272) within the syntaxin 1A transmembrane domain are essential. Synaptotagmin 1, a vesicle-associated protein, accelerated the activation kinetics indicating Ca(v)2.2 coupling to the vesicle. The unique modifications of Ca(v)1.2 and Ca(v)2.2 kinetics by syntaxin 1A, SNAP-25, and synaptotagmin combined implied excitosome formation, a primed fusion complex of the channel with synaptic proteins. The Ca(v)1.2 cytosolic domain Lc(753-893), acted as a dominant negative modulator, competitively inhibiting insulin release of channel-associated vesicles (CAV), the readily releasable pool of vesicles (RRP) in islet cells. A molecular mechanism is offered to explain fast secretion of vesicles tethered to SNAREs-associated Ca2+ channel. The tight arrangement facilitates the propagation of conformational changes induced during depolarization and Ca2+-binding at the channel, to the SNAREs to trigger secretion. The results imply a rapid Ca2+-dependent CAV (RRP) release, initiated by the binding of Ca2+ to the channel, upstream to intracellular Ca2+ sensor thus establishing the Ca2+ channel as the Ca2+ sensor of neurotransmitter release.

The transmembrane domain of syntaxin 1A negatively regulates voltage-sensitive Ca(2+) channels

Syntaxin 1A has a pronounced inhibitory effect on the activation kinetics and current amplitude of voltage-gated Ca(2+) channels. This study explores the molecular basis of syntaxin interaction with N- and Lc-type Ca(2+) channels by way of functional assays of channel gating in a Xenopus oocytes expression system. A chimera of syntaxin 1A and syntaxin 2 in which the transmembrane domain of syntaxin 2 replaced the transmembrane of syntaxin 1A (Sx1-2), significantly reduced the rate of activation of N- and Lc-channels. This shows a similar effect to that demonstrated by syntaxin 1A, though the current was not inhibited. The major sequence differences at the transmembrane of the syntaxin isoforms are that the two highly conserved cysteines Cys 271 and Cys 272 in syntaxin 1A correspond to the valines Val 272 and Val 273 in syntaxin 2 transmembrane. Mutating either cysteines in Sx1-1 (syntaxin 1A) to valines, did not affect modulation of the channel while a double mutant C271/272V was unable to regulate inward current. Transfer of these two cysteines to the transmembrane of syntaxin 2 by mutating Val 272 and Val 273 to Cys 272 and Cys 273 led to channel inhibition. When cleaved by botulinum toxin, the syntaxin 1A fragments, amino acids 1-253 and 254-288, which includes the transmembrane domain, were both unable to inhibit current amplitude but retained the ability to modify the activation kinetics of the channel. A full-length syntaxin 1A and the integrity of the two cysteines within the transmembrane are crucial for coordinating Ca(2+) entry through the N- and Lc-channels. These results suggest that upon membrane depolarization, the voltage-gated N- and Lc-type Ca(2+)-channels signal the exocytotic machinery by interacting with syntaxin 1A at the transmembrane and the cytosolic domains. Cleavage with botulinum toxin disrupts the coupling of the N- and Lc-type channels with syntaxin 1A and abolishes exocytosis, supporting the hypothesis that these channels actively participate in Ca(2+) regulated secretion.

Decreased bone mineral density is common after autologous blood or marrow transplantation

Survivors of autologous blood or marrow transplantation (ABMT) are predisposed to decreased bone mineral density (BMD), but data are lacking on the incidence and risk factors for this condition. Therefore, we measured BMD in 64 of 68 consecutive ABMT survivors (35 men and 29 women) attending the University of Toronto ABMT long-term follow-up clinic. Patients were evaluated a median of 4.2 years (range: 4.9 months-11.4 years) after ABMT. Median age at evaluation was 49.6 years (range: 23.5-68.2 years). At the L1-L4 vertebrae, 17 (26%) patients (eight men and nine women) had osteopenia and one male (2%) had osteoporosis. Mean BMD at L1-L4 did not differ from healthy young adults or age and sex matched controls. At the femoral neck, 30 patients (46%) (18 men and 12 women) had osteopenia and five (8%) (two men and three women) had osteoporosis. Mean BMD at the femoral neck was significantly lower than in healthy young adults and age- and sex-matched controls. By regression analysis, patients with decreased BMD were older than those with normal BMD (P = 0.02). Gender, body mass index, time from BMT to evaluation and presence of hypogonadism were not associated with decreased BMD. Treatment of decreased bone density was instituted and follow-up data were obtained 1 year after treatment in 22 of 39 patients with reduced BMD. Nineteen (86%) patients had stabilization or improvement of their bone density at follow-up. We conclude that, after ABMT, over half of the patients have evidence of osteopenia or osteoporosis. Men and women were equally affected. In our study, only older age at evaluation was predictive for loss of BMD. We recommend the measurement of BMD as an integral component to the follow-up of ABMT patients.

N-type voltage-sensitive calcium channel interacts with syntaxin, synaptotagmin and SNAP-25 in a multiprotein complex

Expression of the N-type voltage sensitive calcium channel in Xenopus oocytes along with syntaxin and p65 showed that the syntaxin-modified N-type channel properties, were fully reversed by p65. The inward current was restored to a significantly higher amplitude when all three proteins were present, suggesting that the channel interacts with syntaxin, p65 and SNAP-25 in a quaternary complex. Further support to a multicomplex formation between the channel and the synaptic proteins was drawn from the steady-state voltage inactivation profiles. A physical interaction of the N-type calcium channel with the vesicular protein synaptotagmin (p65) was demonstrated biochemically, using recombinant fusion proteins. The interaction is confined to a cytosolic channel domain that separates segments II and III amino acids 710-1090 of the N-type channel (N-Loop710-1090). In vitro binding of recombinant N-Loop710-1090 to p65 (amino acids 96-421) involves the two C2 domains of p65, C2A domain [amino acids 96-265; p65(1-3)] and C2B domain [amino acids 248-421; p65(3-5)]. While the binding of C2A and C2B domains was calcium independent, C2B domain binding to the N-Loop was inositol-hexaphosphate (IP6)-sensitive. The N-Loop710-1090 binding to p65 was competed by syntaxin and SNAP-25, which are synaptic plasma membrane proteins. These combined functional and biochemical approaches provide evidence for a complex formation between the N-type channel and the exocytotic machinery which by generating fusion-competent vesicles may function to regulate the process of synaptic secretion.

The voltage sensitive Lc-type Ca2+ channel is functionally coupled to the exocytotic machinery

Although N- and P-type Ca2+ channels predominant in fast-secreting systems, Lc-type Ca2+ channels (C-class) can play a similar role in certain secretory cells and synapses. For example, in retinal bipolar cells, Ca2+ entry through the Lc channels triggers ultrafast exocytosis, and in pancreatic beta-cells, evoked secretion is highly sensitive to Ca2+. These findings suggest that a rapidly release pool of vesicles colocalizes with the Ca2+ channels to allow high Ca2+ concentration and a tight coupling of the Lc channels at the release site. In binding studies, we show that the Lc channel is physically associated with synaptotagmin (p65) and the soluble N-ethylmaleimide-sensitive attachment proteins receptors: syntaxin and synaptosomal-associated protein of 25 kDa. Soluble N-ethylmaleimide-sensitive attachent proteins receptors coexpressed in Xenopus oocytes along with the Lc channel modify the kinetic properties of the channel. The modulatory action of syntaxin can be overcome by coexpressing p65, where at a certain ratio of p65/syntaxin, the channel regains its unaltered kinetic parameters. The cytosolic region of the channel, Lc753-893, separating repeats II-III of its alpha1C subunit, interacts with p65 and "pulls" down native p65 from rat brain membranes. Lc753-893 injected into single insulin-secreting beta-cell, inhibits secretion in response to channel opening, but not in response to photolysis of caged Ca2+, nor does it affect Ca2+ current. These results suggest that Lc753-893 competes with the endogenous channel for the synaptic proteins and disrupts the spatial coupling with the secretory apparatus. The molecular organization of the Lc channel and the secretory machinery into a multiprotein complex (named excitosome) appears to be essential for an effective depolarization evoked exocytosis.

Role of the isoforms of CCAAT/enhancer-binding protein in the initiation of phosphoenolpyruvate carboxykinase (GTP) gene transcription at birth

The gene for phosphoenolpyruvate carboxykinase (PEPCK), a target of CCAAT/enhancer-binding protein-alpha (C/EBPalpha) and -beta (C/EBPbeta), begins to be expressed in the liver at birth. Mice homozygous for a deletion in the gene for CEBPalpha (C/EBPalpha-/- mice) die shortly after birth of hypoglycemia, with no detectable hepatic PEPCK mRNA and negligible hepatic glycogen stores. Half of the mice homozygous for a deletion in the gene for CEBPbeta (C/EBPbeta-/- mice) have normal glucose homeostasis (phenotype A), and the other half die at birth of hypoglycemia due to a failure to express the gene for PEPCK and to mobilize hepatic glycogen (phenotype B). Insulin deficiency induces C/EBPalpha and PEPCK gene transcription in the livers of 19-day fetal rats, whereas dibutyryl cyclic AMP (Bt2cAMP) increases the expression of the gene for C/EBPbeta and causes a transient burst of PEPCK mRNA. Bt2cAMP induces PEPCK mRNA in the livers of fetal C/EBPalpha-/- mice, but at only 20% of the level of control animals; however, there is no induction of PEPCK mRNA if the cyclic nucleotide is injected into C/EBPalpha-/- mice immediately after delivery. The expression of the gene for C/EBPbeta is markedly induced in the livers of C/EBPalpha-/- mice within 2 h after the administration of Bt2cAMP. C/EBPbeta-/- mice injected at 20 days of fetal life with Bt2cAMP have a normal pattern of induction of hepatic PEPCK mRNA. In C/EBPbeta-/- mice with phenotype B, the administration of Bt2cAMP immediately after delivery induces PEPCK mRNA, causes the mobilization of hepatic glycogen, and maintains normal glucose homeostasis for up to 4 h (duration of the experiment). We conclude that C/EBPalpha is required for the cAMP induction of PEPCK gene expression in the liver and that C/EBPbeta can compensate for the loss of C/EBPalpha if its concentration is induced to appropriate levels.

Synaptotagmin restores kinetic properties of a syntaxin-associated N-type voltage sensitive calcium channel

The voltage sensitive N-type calcium channel interacts functionally and biochemically with synaptotagmin (p65). N-type channel interaction with p65 is demonstrated in the Xenopus oocyte expression system, where p65 alters the steady state voltage inactivation of the N-channel, and fully restores the syntaxin-modified current amplitude and inactivation kinetics in a calcium dependent manner. In agreement with the functional results, GST-p65 fusion protein binds to a cytosolic region, amino acids 710-1090 of the N-type channel (N-loop(710-1090)). The results of the combined approach provide a functional and biochemical basis for proposing that p65 interaction with the N-type channel brings p65 into a close association with a syntaxin-coupled channel. In turn, calcium entry through the liberated channel initiates fusion of the primed vesicles with the cell membrane at a short distance from the site of calcium entry.

Identification of differentially expressed genes during hepatocytes development and characterization of their prenatal hormonal induction

Upon birth, the liver acquires new functions as a result of the initiation of expression of key enzymes. One example is the initiation of gluconeogenesis which depends on the induced appearance of phosphoenolpyruvate carboxykinase (P-pyruvate-CK) at birth. To characterize other genes that undergo such regulation, a differential screening was performed on a cDNA library from well-differentiated hepatoma cells. The pattern of tissue-specific and developmental-specific expression was determined for seven genes. Three clones, out of which two encode for the known genes alcohol dehydrogenase class I (ADH) and phenylalanine 4-monooxygenase (PAH) and a new gene (clone 116-3), exhibited a pattern of expression similar to that of the P-pyruvate-CK gene, i.e. their expression was liver and kidney specific and induced in the liver upon birth. Determination of the sequence of clone 116-3 revealed that it belonged to the UDP-glucuronosyltransferases type 2 (UGT2) family and thus was named UGT2B-rH4. To examine whether expression of the various genes could be prematurely induced by hormones in the fetal liver, either high levels of cAMP or low levels of insulin were induced in utero. The results demonstrated that cAMP induced a marked expression only of the genes for P-pyruvate-CK and ADH but not of those for PAH or UGT2B-rH4, while insulin deficiency induced premature expression of all four genes. We suggest that a set of genes whose expression is specifically induced in the liver upon birth can be prematurely induced by the hormones in utero.

The alpha 2/delta subunit of voltage sensitive Ca2+ channels is a single transmembrane extracellular protein which is involved in regulated secretion

The membrane topology of alpha 2/delta subunit was investigated utilizing electrophysiological functional assay and specific anti-alpha 2 antibodies. (a) cRNA encoding a deleted alpha 2/delta subunit was coinjected with alpha 1C subunit of the L-type calcium channel into Xenopus oocytes. The truncated form, lacking the third putative TM domain (alpha 2/delta delta TMIII), failed to amplify the expressed inward currents, normally induced by alpha 1C coinjected with intact alpha 2/delta subunit. Western blot analysis of alpha 2/delta delta TMIII shows the appearance of a degraded alpha 2 protein and no expression of the full-size two-TM truncated-protein. The improper processing of alpha 2/delta delta TMIII suggests that the alpha 2/delta is a single TM domain protein and the TM region is positioned at the delta subunit. (b) External application of anti-alpha 2 antibodies, prepared for an epitope within the alternatively spliced and 'intracellular' region, inhibits depolarization induced secretion in PC12, further supporting an external location of the alpha 2 subunit and establishing delta subunit as the only membrane anchor for the extracellular alpha 2 subunit.

Identification of the alternative spliced form of the alpha 2/delta subunit of voltage sensitive Ca2+ channels expressed in PC12 cells

The alpha 2/delta subunit of voltage sensitive Ca2+ channels expressed in PC12 has been cloned and partially sequenced. The message observed in Northern blot analysis displays a 7.5 kb transcript, identical in size to mRNA of rabbit skeletal muscle and rat brain. The nucleotide sequence of the cloned alpha 2 subunit of the PC12 specific cDNA is > 99% identical to rat brain sequence and 85% to skeletal muscle. Reverse-transcriptase-polymerase chain reaction (RT-PCR) of the alternative splicing region identifies two deleted regions of 57 bp and 21 bp in PC12 expressed alpha 2/delta transcript. The alternative variant alpha 2e of alpha 2/delta subunit which is expressed in PC12 cells was previously identified in human embryonic kidney (HEK293) cells. RT-PCR analysis show two different sized alternative PCR fragments in rat lung and none in rat spleen, kidney and intestine. Antibodies prepared against a 19 amino acid peptide within the alternative spliced region effectively inhibits [3H]dopamine release in PC12 cells. This implies that the alternatively spliced region is positioned extracellularly and is involved in regulation of the L-type Ca2+ channel-mediated transmitter release.

Transcriptional regulation of the phosphoenolpyruvate carboxykinase gene by cooperation between hepatic nuclear factors

To study the transcriptional regulation of the liver gluconeogenic phenotype, the underdifferentiated mouse Hepa-1c1c7 (Hepa) hepatoma cell line was used. These cells mimicked the fetal liver by appreciably expressing the alpha-fetoprotein and albumin genes but not the phosphoenolpyruvate carboxykinase (PEPCK) gene. Unlike the fetal liver, however, Hepa cells failed to express the early-expressed factors hepatocyte nuclear factor 1 alpha (HNF-1 alpha) and HNF-4 and the late-expressed factor C/EBP alpha, thereby providing a suitable system for examining possible cooperation between these factors in the transcriptional regulation of the PEPCK gene. Transient transfection assays of a chimeric PEPCK-chloramphenicol acetyltransferase construct showed a residual PEPCK promoter activity in the Hepa cell line, which was slightly stimulated by cotransfection with a single transcription factor from either the C/EBP family or HNF-1 alpha but not at all affected by cotransfection of HNF-4. In contrast, cotransfection of the PEPCK construct with members from the C/EBP family plus HNF-1 alpha resulted in a synergistic stimulation of the PEPCK promoter activity. This synergistic effect depended on the presence in the PEPCK promoter region of the HNF-1 recognition sequence and on the presence of two C/EBP recognition sequences. The results demonstrate a requirement for coexistence and cooperation between early and late liver-enriched transcription factors in the transcriptional regulation of the PEPCK gene. In addition, the results suggest redundancy between members of the C/EBP family of transcription factors in the regulation of PEPCK gene expression.

Cis-regulatory elements that confer differential expression upon the rat gene encoding phosphoenolpyruvate carboxykinase in kidney and liver

The PCK gene, encoding cytosolic phosphoenolpyruvate carboxykinase, is specifically expressed in gluconeogenic tissues, liver and kidney. Hence it serves as a model of a class of single-copy genes whose transcription is restricted to a few tissues, rather than a unique tissue. To begin delineating the mechanisms that govern this pattern of expression, cis-regulatory elements of PCK were examined using transient transfection assays in PCK-expressing kidney and hepatoma cell lines. The analyses enabled us to identify a proximal element, between nucleotide (nt) positions -121 and -98, relative to the transcription start point that is sufficient for specific expression in kidney cells, but is just one of the elements required for expression in hepatoma cells. A distal element (between nt -487 and -417), which is essential for hepatoma-specific expression, is not needed in kidney cells. We suggest that the differential regulation of PCK expression in the liver and kidney results from an interplay between different cis-regulatory elements and trans-acting factors.

Developmentally regulated interactions of liver nuclear factors with the rat phosphoenolpyruvate carboxykinase promoter

A sequential pattern of interactions of trans-acting factors in rat liver with the phosphoenolpyruvate carboxykinase promoter during late development was observed. A liver-enriched factor, possibly AF1, interacted with the promoter in fetal liver, whereas a factor with the characteristics of C/EBP bound the promoter after birth with the onset of the gene expression.

Repetitive structure in the long-terminal-repeat element of a type II human T-cell leukemia virus

The majority of human T-cell leukemia virus isolates (HTLV-I) are associated with clinically aggressive adult T-cell leukemia/lymphomas. By contrast, HTLV-II has been isolated from a patient with a relatively benign hairy T-cell leukemia. To characterize differences in the viral genomes that might contribute to these different pathologies, we determined the nucleotide sequence of the long terminal repeat (LTR) of a HTLV-II provirus. Comparison with the type I HTLV LTR reveals that, whereas the overall structural features are similar, the two sequences differ markedly throughout most of the length of the LTR. Despite the overall differences, the sequences of several functional regions of the two LTRs are conserved. These include the 5' boundary of U3, the RNA cap site, and the tRNAPro-binding site immediately 3' to the LTR. Another point of similarity is a 21-base sequence that is repeated four times in the U3 region of HTLV-II and three times in the U3 region of HTLV-I. This sequence has a formal analogy to, but no common sequence with, viral transcriptional enhancers. The U3 region of HTLV-II possesses a series of imperfect tandem direct repeats, 42 bases long, 21 bases long, 19 bases long, and 7 bases long. These structures differ from those of HTLV-I except for the 21-base repeat sequence. Thus, the structure of HTLV-II differs substantially from that of HTLV-I in the region that governs transcriptional initiation and tissue specificity. Such differences may account for some of the differences in clinical presentation of HTLV-associated adult T-cell leukemia/lymphomas and hairy T-cell leukemia.

Effects of glucose on insulin release and on intermediary metabolism of isolated perifused pancreatic islets from fed and fasted rats

We examined the relationship between glucose-induced insulin release and the intermediary metabolism of islets from fed and fasted rats. Isolated islets were perifused and insulin release measured in the effluent. At various times after switching islets from 2.4 to 8.6 or 14.5 mM glucose or from 2.4 to 14.5 and back to 2.4 mM glucose, islets were quickly frozen, freeze dried, and subsequently analyzed for tissue content of glucose-6-P, fructose-1,6-P2 plus triose-P, Pi, ATP, ADP, 5'-AMP, NADH, NADPH, total NAD, and total NADP using enzymatic fluorometric procedures. When islets from fed rats were exposed to high glucose, there were concomitant increases of insulin release and islet content of glucose-6-P, fructose-1,6-P2 plus triose-P, NADH, and NADPH. During stimulation Pi and 5'-AMP content fell markedly. The total adenine nucleotide content remained constant. Similar secretory and metabolic changes occurred when 1.5 mM Pi was added to the perifusion fluid. When glucose-stimulated islets were switched back to low glucose for 10 min, all substances but fructose-1,6-P2 plus triose-P, 5'-AMP, NADPH, and possibly ATP returned to the prestimulatory level. Starvation of rats for 3 days blocked the secretory response to 8.6 mM glucose. Fructose-1,6-P2 plus triose-P rose but it did not attain the level existing in islets from fed rats. The ratios (ATP)/(5'-AMP) and (ATP)/(Pi)(adp) increased to the values observed in glucose-stimulated islets of fed rats. The metabolic changes in islets from fed rats exposed to high glucose are consistent with an activation of glycolysis occurring concomitantly with stimulated rates of insulin release. This occurs despite the decrease of important activators of glycolysis--Pi and 5'-AMP. The enhanced glycolysis possibly results from P-fructokinase activation by increased fructose-6-P levels. Activation of glycolysis with 8.6 mM glucose was not as pronounced in islets from starved rats. Despite the different secretory response of islets from fet and fasted rats, the changes of phosphorylation state in the islets, in particular, Pi and 5'-AMP levels, were similar.

Alterations in pancreatic islet phosphate content during secretory stimulation with glucose

Isolated rat pancreatic islets were perifused and analyzed for phosphate content immediately following the transient increase in the efflux of orthophosphate which occurs when insulin secretion is stimulated by glucose. In some instances, islets were perifused directly following isolation to minimize preparative delay; in others, islets were prelabeled during incubation with [32P]orthophosphate for 90 min prior to perifusion. In both experimental situations, total islet phosphate content declined 40--50% following exposure to stimulating concentrations of glucose and initiation of enhanced insulin release. In the experiments with prelabeled islets, tissue content of [32P]orthophosphate fell to a similar extent so that the specific radioactivity of islet orthophosphate was unaffected. Inhibited of heightened insulin release with Ni2+ did not modify the decrements in total or radioactive tissue orthophosphate, thus indicating that these responses to islet stimulation reflect events which are proximal to activated exocytosis. Simultaneous analyses for tissue ATP and ADP demonstrated that the efflux in orthophosphate and reduction in tissue orthophosphate content were not mediated via net changes in islet adenine nucleotides. The observations represent the first documentation that a net reduction of tissue inorganic phosphate is one of the early components of stimulus-secretion coupling in isolated pancreatic islets.