Navigating the Blood-Brain Barrier: Challenges and Therapeutic Strategies in Breast Cancer Brain Metastases

Breast cancer (BC) is the most common cancer in women, with metastatic BC being responsible for the highest number of deaths. A frequent site for BC metastasis is the brain. Brain metastasis derived from BC involves the cooperation of multiple genetic, epigenetic, angiogenic, and tumor-stroma interactions. Most of these interactions provide a unique opportunity for development of new therapeutic targets. Potentially targetable signaling pathways are Notch, Wnt, and the epidermal growth factor receptors signaling pathways, all of which are linked to driving BC brain metastasis (BCBM). However, a major challenge in treating brain metastasis remains the blood-brain barrier (BBB). This barrier restricts the access of unwanted molecules, cells, and targeted therapies to the brain parenchyma. Moreover, current therapies to treat brain metastases, such as stereotactic radiosurgery and whole-brain radiotherapy, have limited efficacy. Promising new drugs like phosphatase and kinase modulators, as well as BBB disruptors and immunotherapeutic strategies, have shown the potential to ease the disease in preclinical studies, but remain limited by multiple resistance mechanisms. This review summarizes some of the current understanding of the mechanisms involved in BC brain metastasis and highlights current challenges as well as opportunities in strategic designs of potentially successful future therapies.

Comparison of Fixation Methods for the Detection of Claudin 1 and E-Cadherin in Breast Cancer Cell Lines by Immunofluorescence

The tight junction membrane protein claudin 1 and the adherens junction protein E-cadherin play critical roles in cell-cell communication and in cell signaling. As a result, their protein levels and distribution in cancer have been a focus of cancer researchers in recent years. The loss of sensitivity to contact inhibition and the establishment of invasive properties in cancer are thought to be a result of the mislocalization of these membrane proteins to the cytoplasm. However, reports on their distribution and levels have been inconsistent. It is therefore critical that the techniques used to determine the cellular localization of these proteins be both consistent and reliable. This study was undertaken to determine the optimal fixation method, methanol or formalin, for the detection of claudin 1 and E-cadherin by immunofluorescence in five different human breast cancer cell lines. Both methods exhibited staining of the cell membrane and cytoplasm, but the strongest and most distinct signals were obtained using methanol fixation. Interestingly, cell-specific differences were also observed that appeared to be associated with levels of claudin 1 and E-cadherin as seen by Western blotting. Therefore, when evaluating cellular localization of the junction proteins claudin 1 and E-cadherin, expression level and cell type differences must be considered.

A Cardiac Mitochondrial FGFR1 Mediates the Antithetical Effects of FGF2 Isoforms on Permeability Transition

Mitochondria, abundant organelles in high energy demand cells such as cardiomyocytes, can determine cell death or survival by regulating the opening of mitochondrial permeability transition pore, mPTP. We addressed the hypothesis that the growth factor FGF2, known to reside in intracellular locations, can directly influence mitochondrial susceptibility to mPTP opening. Rat cardiac subsarcolemmal (SSM) or interfibrillar (IFM) mitochondrial suspensions exposed directly to rat 18 kDa low molecular weight (Lo-) FGF2 isoform displayed increased resistance to calcium overload-induced mPTP, measured spectrophotometrically as "swelling", or as cytochrome c release from mitochondria. Inhibition of mitochondrial protein kinase C epsilon abrogated direct Lo-FGF2 mito-protection. Exposure to the rat 23 kDa high molecular weight (Hi) FGF2 isoform promoted cytochrome c release from SSM and IFM under nonstressed conditions. The effect of Hi-FGF2 was prevented by mPTP inhibitors, pre-exposure to Lo-FGF2, and okadaic acid, a serine/threonine phosphatase inhibitor. Western blotting and immunoelectron microscopy pointed to the presence of immunoreactive FGFR1 in cardiac mitochondria in situ. The direct mito-protective effect of Lo-FGF2, as well as the deleterious effect of Hi-FGF2, were prevented by FGFR1 inhibitors and FGFR1 neutralizing antibodies. We propose that intracellular FGF2 isoforms can modulate mPTP opening by interacting with mito-FGFR1 and relaying isoform-specific intramitochondrial signal transduction.

The Breast Tumor Microenvironment: A Key Player in Metastatic Spread

The tumor microenvironment plays a pivotal role in the tumorigenesis, progression, and metastatic spread of many cancers including breast. There is now increasing evidence to support the observations that a bidirectional interplay between breast cancer cells and stromal cells exists within the tumor and the tumor microenvironment both at the primary tumor site and at the metastatic site. This interaction occurs through direct cell to cell contact, or by the release of autocrine or paracrine factors which can activate pro-tumor signaling pathways and modulate tumor behavior. In this review, we will highlight recent advances in our current knowledge about the multiple interactions between breast cancer cells and neighboring cells (fibroblasts, endothelial cells, adipocytes, innate and adaptive immune cells) in the tumor microenvironment that coordinate to regulate metastasis. We also highlight the role of exosomes and circulating tumor cells in facilitating breast cancer metastasis. We discuss some key markers associated with stromal cells in the breast tumor environment and their potential to predict patient survival and guide treatment. Finally, we will provide some brief perspectives on how current technologies may lead to the development of more effective therapies for the clinical management of breast cancer patients.

Abstract 838: High Molecular Weight FGF2 Contributes to Pressure Overload Induced Systolic Dysfunction by a Mechanism Associated With Modulation of the NR1D1 Orphan Nuclear Receptor Expression

Fibroblast growth factor 2 (FGF2) is implicated in normal cardiac development as well as cardiac pathophysiology; however, FGF2 exist as multiple high and low molecular weight isoforms. While endogenous low molecular weight FGF2 (Lo-FGF2) is cardioprotective during chronic stress, the more prevalent endogenous high molecular weight FGF2 (Hi-FGF2) is proposed to promote maladaptive cardiac remodeling. We have investigated the hypothesis that genetic elimination of Hi-FGF attenuates cardiac dysfunction in mice that have been subjected to pressure overload by transverse aortic constriction (TAC).

Two groups of male C57BL/6mice were compared: (1) Wild type (WT) mice, expressing Hi- and Lo-FGF2 (FGF[WT] mice); and (2) Hi-FGF2 knock-out mice, expressing only Lo-FGF2 (FGF[Lo] mice). Echocardiographic assessment of heart function and dimensions was done at baseline and then 4 and 8 weeks after TAC or sham surgery. FGF[WT] mice displayed a decline in systolic function compared to their corresponding sham animals at 4- and 8-weeks post-TAC, which was absent in the FGF[Lo] mice. Relative levels of B-type natriuretic peptide, a marker of cardiac pathology severity, were elevated in FGF[WT] but not FGF[Lo] mice compared to shams. Increased accumulation of the pro-cell death protein BCL2/adenovirus E1B 19 kDa protein-interacting protein-3 was more pronounced in the FGF(WT) compared to FGF(Lo) mice, post TAC. Microarray analysis of the whole transcriptome of hearts in FGF2[WT] and FGF2[Lo] mice indicated the pathway linked to circadian rhythm as a candidate for the most significant differentially regulated. Specifically, upregulation of the circadian rhythm master regulator, Nuclear Receptor Subfamily 1 Group D Member 1 (NR1D1), was validated by qPCR and protein immunoblotting in FGF[Lo] mice versus downregulation of NR1D1in FGF[WT] mice post-TAC, when compared to their sham operated littermates.

Taken together these studies suggest that expression of Hi-FGF2 contributes to cardiac systolic dysfunction in left ventricular pressure overloaded WT mice by downregulation of Nr1D1, post-TAC.

Non-mitogenic FGF2 protects cardiomyocytes from acute doxorubicin-induced toxicity independently of the protein kinase CK2/heme oxygenase-1 pathway

Doxorubicin (Dox)-induced cardiotoxicity, a limiting factor in the use of Dox to treat cancer, can be mitigated by the mitogenic factor FGF2 in vitro, via a heme oxygenase 1 (HO-1)-dependent pathway. HO-1 upregulation was reported to require protein kinase CK2 activity. We show that a mutant non-mitogenic FGF2 (S117A-FGF2), which does not activate CK2, is cardioprotective against acute cardiac ischemic injury. We now investigate the potential of S117A-FGF2 to protect cardiomyocytes against acute Dox injury and decrease Dox-induced upregulation of oxidized phospholipids. The roles of CK2 and HO-1 in cardiomyocyte protection are also addressed.Rat neonatal cardiomyocyte cultures were used as an established in vitro model of acute Dox toxicity. Pretreatment with S117A-FGF2 protected against Dox-induced: oxidative stress; upregulation of fragmented and non-fragmented oxidized phosphatidylcholine species, measured by LC/MS/MS; and cardiomyocyte injury and cell death measured by LDH release and a live-dead assay. CK2 inhibitors (TBB and Ellagic acid), did not affect protection by S117A-FGF2 but prevented protection by mitogenic FGF2. Furthermore, protection by S117A-FGF2, unlike that of FGF2, was not prevented by HO-1 inhibitors and S117A-FGF2 did not upregulate HO-1. Protection by S117A-FGF2 required the activity of FGF receptor 1 and ERK.We conclude that mitogenic and non-mitogenic FGF2 protect from acute Dox toxicity by common (FGFR1) and distinct, CK2/HO-1- dependent or CK2/HO-1-independent (respectively), pathways. Non-mitogenic FGF2 merits further consideration as a preventative treatment against Dox cardiotoxicity.

Elimination or neutralization of endogenous high-molecular-weight FGF2 mitigates doxorubicin-induced cardiotoxicity

Cardiac fibroblast growth factor 2 (FGF2) exerts multiple paracrine activities related to cardiac response to injury. Endogenous FGF2 is composed of a mixture of 70% high- and 30% low-molecular-weight isoforms (Hi-FGF2 and Lo-FGF2, respectivley); although exogenously added Lo-FGF2 is cardioprotective, the roles of endogenous Hi-FGF2 or Lo-FGF2 have not been well defined. Therefore, we investigated the effect of elimination of Hi-FGF2 expression on susceptibility to acute cardiac damage in vivo caused by an injection of the genotoxic drug doxorubicin (Dox). Mice genetically depleted of endogenous Hi-FGF2 and expressing only Lo-FGF2 [FGF2(Lo) mice] were protected from the Dox-induced decline in ejection fraction displayed by their wild-type FGF2 [FGF2(WT)] mouse counterparts, regardless of sex, as assessed by echocardiography for up to 10 days post-Dox treatment. Because cardiac FGF2 is produced mainly by nonmyocytes, we next addressed potential contribution of fibroblast-produced FGF2 on myocyte vulnerability to Dox. In cocultures of neonatal rat cardiomyocytes (r-cardiomyocytes) with mouse fibroblasts from FGF2(WT) or FGF2(Lo) mice, only the FGF2(Lo)-fibroblast cocultures protected r-cardiomyocytes from Dox-induced mitochondrial and cellular damage. When r-cardiomyocytes were cocultured with or exposed to conditioned medium from human fibroblasts, neutralizing antibodies for human Hi-FGF-2, but not total FGF2, mitigated Dox-induced injury of cardiomyocytes. We conclude that endogenous Hi-FGF2 reduces cardioprotection by endogenous Lo-FGF2. Antibody-based neutralization of endogenous Hi-FGF2 may offer a prophylactic treatment against agents causing acute cardiac damage. NEW & NOTEWORTHY Cardiomyocytes, in vivo and in vitro, were protected from the deleterious effects of the anticancer drug doxorubicin by the genetic elimination or antibody-based neutralization of endogenous paracrine high-molecular-weight fibroblast growth factor 2 isoforms. These findings have a translational potential for mitigating doxorubicin-induced cardiac damage in patients with cancer by an antibody-based treatment.

Fibroblast growth factor-2-mediated protection of cardiomyocytes from the toxic effects of doxorubicin requires the mTOR/Nrf-2/HO-1 pathway

Background

Cardiotoxic side effects impose limits to the use of anti-tumour chemotherapeutic drugs such as doxorubicin (Dox). There is a need for cardioprotective strategies to prevent the multiple deleterious effects of Dox. Here, we examined the ability of administered fibroblast growth factor-2 (FGF-2), a cardioprotective protein that is synthesized as high and low molecular weight (Hi-, Lo-FGF-2) isoforms, to prevent Dox-induced: oxidative stress; cell death; lysosome dysregulation; and inactivation of potent endogenous protective pathways, such as the anti-oxidant/detoxification nuclear factor erythroid-2-related factor (Nrf-2), heme oxygenase-1 (HO-1) axis.

Methods and Results

Brief pre-incubation of neonatal rat cardiomyocyte cultures with either Hi- or Lo-FGF-2 reduced the Dox-induced: oxidative stress; apoptotic/necrotic cell death; lysosomal dysregulation; decrease in active mammalian target of Rapamycin (mTOR). FGF-2 isoforms prevented the Dox-induced downregulation of Nrf-2, and promoted robust increases in the Nrf-2-downstream targets including the cardioprotective protein HO-1, and p62/SQSTM1, a multifunctional scaffold protein involved in autophagy. Chloroquine, an autophagic flux inhibitor, caused a further increase in p62/SQSTM1, indicating intact autophagic flux in the FGF-2-treated groups. A selective inhibitor for HO-1, Tin-Protoporphyrin, prevented the FGF-2 protection against cell death. The mTOR inhibitor Rapamycin prevented FGF-2 protection, and blocked the FGF-2 effects on Nrf-2, HO-1 and p62/SQSTM1.

Conclusions

In an acute setting Hi- or Lo-FGF-2 protect cardiomyocytes against multiple Dox-induced deleterious effects, by a mechanism dependent on preservation of mTOR activity, Nrf-2 levels, and the upregulation of HO-1. Preservation/activation of endogenous anti-oxidant/detoxification defences by FGF-2 is a desirable property in the setting of Dox-cardiotoxicity.

Abstract 374: FGF2 Isoform-selective as well as Non-selective Signals Protect Cardiomyocytes from Doxorubicin-induced Cell Death

Introduction: Doxorubicin (DOX) induced cardiotoxicity, including cardiomyocyte cell death, remains a major challenge for anticancer therapies. DOX can disrupt the balance between synthesis and degradation systems by affecting major cellular signaling pathways including the mammalian target of Rapamycin (mTOR), and AMP-activated kinase (AMPK). Fibroblast Growth Factor 2 (FGF2), a multifunctional protein expressed by heart cells and downregulated by DOX, consists of two types of isoforms, low molecular weight, Lo-FGF2, (~18 kDa) and high molecular weight, Hi-FGF2, (>20 kDa), displaying isoform-selective and non-selective properties. We have studied the effects of added FGF2 isoforms on DOX induced dysregulation of signaling pathways impacting on cardiomyocyte survival and autophagy.

Methods and Results: Primary cultures of neonatal rat cardiomyocytes were subjected to 0.5 μM DOX in the absence or presence of pretreatment with FGF2 isoforms, at 10 ng/ml. Both Hi- and Lo- FGF2 decreased DOX-induced injury and cell death, measured by LDH release, a Live-Dead assay, and activation of caspase 3. Neither isoform prevented the DOX-induced cell death in MCF7 cells, a breast cancer cell line. In myocytes, both isoforms prevented the DOX-induced downregulation of mTORC1 activity (phospho-Ser2448). The mTOR inhibitor Rapamycin prevented the beneficial effects of FGF2. Hi-FGF2, but not Lo-FGF2, significantly increased AMPK activity (phospho-Thr172) pre- and post-DOX. Compound C, an inhibitor of AMPK, prevented the protective effect of Hi- , but not Lo-, FGF2. To assess autophagy, cardiomyocytes were transduced with an adenoviral vector for GFP-LC3. Numbers of GFP-LC3 aggregates (dots) per cell were measured, and suggested that both Hi- and Lo-FGF2 prevented the DOX-induced increases in autophagy and autophagy flux, as also indicated by increased levels of p62 post-DOX in the presence of FGF2. Pharmacological inhibition of autophagy by 3-Methyladenine was protective against DOX.

Conclusions: FGF2 isoforms protect cardiomyocytes against acute DOX damage, by activating mTORC1 (both Hi or Lo FGF2), as well as, in the case of Hi-FGF2, the AMPK pathway. Protection by FGF2 isoforms was associated with prevention of accelerated flux.

Abstract 165: The 18 kDa FGF-2 Prevents the Doxorubicin-induced Cardiac Damage and Amp-activated Kinase Activation, in vitro and in vivo

Introduction: Protection of the heart from chemotherapeutic (Doxorubicin, DOX) drug-induced toxicity is a desirable goal, to limit side effects of cancer treatments. DOX toxicity has been linked to the activation (phosphorylation) of the AMP-activated kinase, AMPK. The 18 kDa low molecular weight isoform of fibroblast growth factor 2 (Lo-FGF-2) is a known cardioprotective and cytoprotective agent. In this study we have tested the ability of Lo-FGF-2 to protect from DOX-induced damage in rat cardiomyocytes in vitro, and in transgenic mouse models in vivo, in relation to AMPK activation.

Methods: Rat neonatal cardiomyocytes in culture were exposed to DOX (0.5 μM) in the presence or absence of pre-treatment Lo-FGF-2 (10 ng/ml). Compound C was used to block phosphorylation (activity) of AMPK. Levels of cell viability/death (using Calcein-AM/Propidium iodide assay), phospho -and total AMPK, and apoptotic markers such as active caspase 3 were analyzed. In addition, transgenic mice expressing only Lo-FGF2, and wild type mice, expressing both high molecular weight (Hi-FGF2) as well as Lo-FGF2 were subjected to DOX injection (20 mg/kg, intraperitoneal); echocardiography was used to examine cardiac function at baseline and at 10 days post-DOX.

Results: DOX-induced cell death of cardiomyocytes in culture was maximal at 24 hours post-DOX coinciding with significantly increased in activated (phosphorylated) AMPK. Compound C attenuated DOX-induced cardiomyocyte loss. Pre-incubation with Lo-FGF-2 decreased DOX induced cell death, and also attenuated the phosphorylation of AMPK post-DOX. Relative levels of phospho-AMPK were lower in the hearts of Lo-FGF2-expressing male mice compared to wild type. DOX-induced loss of contractile function (left ventricular ejection fraction and endocardial velocity) was negligible in Lo-FGF2-expressing mice but significant in wild type mice.

Conclusion: Lo-FGF-2 protects the heart from DOX-induced damage in vitro and in vivo, by a mechanism likely involving an attenuation of AMPK activity.

High molecular weight fibroblast growth factor-2 in the human heart is a potential target for prevention of cardiac remodeling

Fibroblast growth factor 2 (FGF-2) is a multifunctional protein synthesized as high (Hi-) and low (Lo-) molecular weight isoforms. Studies using rodent models showed that Hi- and Lo-FGF-2 exert distinct biological activities: after myocardial infarction, rat Lo-FGF-2, but not Hi-FGF-2, promoted sustained cardioprotection and angiogenesis, while Hi-FGF-2, but not Lo-FGF-2, promoted myocardial hypertrophy and reduced contractile function. Because there is no information regarding Hi-FGF-2 in human myocardium, we undertook to investigate expression, regulation, secretion and potential tissue remodeling-associated activities of human cardiac (atrial) Hi-FGF-2. Human patient-derived atrial tissue extracts, as well as pericardial fluid, contained Hi-FGF-2 isoforms, comprising, respectively, 53%(±20 SD) and 68% (±25 SD) of total FGF-2, assessed by western blotting. Human atrial tissue-derived primary myofibroblasts (hMFs) expressed and secreted predominantly Hi-FGF-2, at about 80% of total. Angiotensin II (Ang II) up-regulated Hi-FGF-2 in hMFs, via activation of both type 1 and type 2 Ang II receptors; the ERK pathway; and matrix metalloprotease-2. Treatment of hMFs with neutralizing antibodies selective for human Hi-FGF-2 (neu-AbHi-FGF-2) reduced accumulation of proteins associated with fibroblast-to-myofibroblast conversion and fibrosis, including α-smooth muscle actin, extra-domain A fibronectin, and procollagen. Stimulation of hMFs with recombinant human Hi-FGF-2 was significantly more potent than Lo-FGF-2 in upregulating inflammation-associated proteins such as pro-interleukin-1β and plasminogen-activator-inhibitor-1. Culture media conditioned by hMFs promoted cardiomyocyte hypertrophy, an effect that was prevented by neu-AbHi-FGF-2 in vitro. In conclusion, we have documented that Hi-FGF-2 represents a substantial fraction of FGF-2 in human cardiac (atrial) tissue and in pericardial fluid, and have shown that human Hi-FGF-2, unlike Lo-FGF-2, promotes deleterious (pro-fibrotic, pro-inflammatory, and pro-hypertrophic) responses in vitro. Selective targeting of Hi-FGF-2 production may, therefore, reduce pathological remodelling in the human heart.

Calreticulin induces dilated cardiomyopathy

BACKGROUND

Calreticulin, a Ca(2+)-buffering chaperone of the endoplasmic reticulum, is highly expressed in the embryonic heart and is essential for cardiac development. After birth, the calreticulin gene is sharply down regulated in the heart, and thus, adult hearts have negligible levels of calreticulin. In this study we tested the role of calreticulin in the adult heart.

METHODOLOGY/PRINCIPAL FINDINGS

We generated an inducible transgenic mouse in which calreticulin is targeted to the cardiac tissue using a Cre/loxP system and can be up-regulated in adult hearts. Echocardiography analysis of hearts from transgenic mice expressing calreticulin revealed impaired left ventricular systolic and diastolic function and impaired mitral valve function. There was altered expression of Ca(2+) signaling molecules and the gap junction proteins, Connexin 43 and 45. Sarcoplasmic reticulum associated Ca(2+)-handling proteins (including the cardiac ryanodine receptor, sarco/endoplasmic reticulum Ca(2+)-ATPase, and cardiac calsequestrin) were down-regulated in the transgenic hearts with increased expression of calreticulin.

CONCLUSIONS/SIGNIFICANCE

We show that in adult heart, up-regulated expression of calreticulin induces cardiomyopathy in vivo leading to heart failure. This is due to an alternation in changes in a subset of Ca(2+) handling genes, gap junction components and left ventricle remodeling.

Abstract P210: Human Atrial Nonmyocytes Secrete Prohypertrophic, High-Molecular-Weight FGF-2, Which Is Upregulated by Angiotensin II via AT-1 and AT-2 Receptors, as Well as ERK and MMP Activation

Background: Very little is known about the expression and role of fibroblast growth factor-2 (FGF-2) isoforms in the human heart. Using the rat model we have documented that high molecular weight Hi-FGF-2 rather than the commonly studied 18 kDa low molecular weight isoform Lo-FGF-2 is a potent inducer of cardiac hypertrophy in vitro and in vivo ; and that Hi-FGF-2 is expressed and secreted predominantly by cardiac non-myocytes (fibroblasts). We have now examined (i) the expression of Hi-FGF-2 in adult human heart (atria) and heart-derived non-myocytes (HDNM), and; (ii) signals regulating Hi-FGF-2 expression in HDNM.

Methods/Results: Atrial tissue, obtained from patients undergoing cardiac surgery, (blinded study), was used to obtain extracts, and to isolate migratory cells (fibroblastic, HDNM). All tissue extracts (n=30) contained Hi- as well as Lo-FGF-2, assessed by Western blotting. Amounts of total FGF-2 varied from 1.5 - 25.5 pg per µg of extracted protein. Immunohistochemistry of paraffin-embedded atrial tissue sections and immunofluorescence of HDNM illustrated that human Hi-FGF-2 is localized mainly in the nucleus but is also present in cytoplasm. As was the case with rat- (ventricle and/or atria) derived fibroblasts, HDNM expressed predominantly Hi-FGF-2 (90% of total). The expression/secretion of Hi-FGF-2 by HDNM, as well as by human embryonic heart-derived fibroblasts, was significantly up-regulated by angiotensin II (Ang II). Simultaneous inhibition of both AT-1 as well as AT-2 receptors (by losartan and PD123319, respectively) was required to fully prevent Ang II-induced Hi-FGF-2 up-regulation. In addition, both inhibition of ERK activation (by U0126), or MMP activity (by MMP-2 Inhibitor I) fully prevented Ang II-induced up-regulation of human Hi-FGF-2.

Conclusions: We have shown for the first time that human heart-derived fibroblastic cells express and secrete pro-hypertrophic Hi-FGF-2 in culture; and thus are likely to do so in vivo . Our data also suggest that the beneficial effects of drugs targeting Ang II signal transduction may be due, in part to their effects on Hi-FGF-2 accumulation.

Connexin43 phosphorylation and cytoprotection in the heart

The fundamental role played by connexins including connexin43 (Cx43) in forming intercellular communication channels (gap junctions), ensuring electrical and metabolic coupling between cells, has long been recognized and extensively investigated. There is also increasing recognition that Cx43, and other connexins, have additional roles, such as the ability to regulate cell proliferation, migration, and cytoprotection. Multiple phosphorylation sites, targets of different signaling pathways, are present at the regulatory, C-terminal domain of Cx43, and contribute to constitutive as well as transient phosphorylation Cx43 patterns, responding to ever-changing environmental stimuli and corresponding cellular needs. The present paper will focus on Cx43 in the heart, and provide an overview of the emerging recognition of a relationship between Cx43, its phosphorylation pattern, and development of resistance to injury. We will also review our recent work regarding the role of an enhanced phosphorylation state of Cx43 in cardioprotection. This article is part of a Special Issue entitled: The Communicating junctions, composition, structure and characteristics.

The role of connexins in controlling cell growth and gene expression

The purpose of this paper is to provide a brief overview of current thinking on the role of connexins, in particular Cx43, in growth regulation, and a more detailed discussion as to potential mechanisms involved with an emphasis on gene expression. While the precise molecular mechanism by which connexins can affect the growth of normal or tumor cells remains elusive, a number of exciting reports have expanded our understanding and are presented in some detail. Thus, we will discuss (Section 2): the role of protein-protein interactions in integrating connexins into multiple signal transduction pathways; phosphorylation at specific sites and reversal of growth inhibition; the role of the carboxy-terminal regulatory domain as a signaling molecule. Some of our latest work on the potential functions of endogenously produced carboxy-terminal fragments of Cx43 are also presented (Section 3). Finally, Section 4 will pay tribute to the rapidly emerging realization that connexins such as Cx43 and Cx32 exert important and extensive effects on gene expression, particularly those genes linked to growth regulation.

Administration of FGF-2 to the heart stimulates connexin-43 phosphorylation at protein kinase C target sites

Fibroblast growth factor-2 (FGF-2) confers acute, preconditioning-like cardiac resistance to ischemic injury in a protein kinase C (PKC)-dependent fashion. One of the downstream targets of PKC is the gap junction protein connexin-43 (Cx43). We thus examined the effects of FGF-2 on Cx43 phosphorylation at specific PKC sites in the adult heart. Rat hearts perfused ex vivo for 20 min with an FGF-2-containing solution displayed increased levels of phosphorylated 44-45 kDa Cx43, assessed by western blotting. In addition, FGF-2 significantly upregulated phosphorylation of the PKC target serines 262 and 368 on Cx43 at intercalated disks, assessed using phosphospecific antibodies in immunolocalization and western blotting assays. Our data show that FGF-2, administered by perfusion, can alter the phosphorylation status of Cx43 at cardiomyocyte intercalated disks, and suggest a link between phosphorylation of Cx43 at specific PKC sites and FGF-2 cardioprotection.

Inhibition of TGFbeta signaling potentiates the FGF-2-induced stimulation of cardiomyocyte DNA synthesis

OBJECTIVE

Added transforming growth factor beta (TGFbeta) inhibits the proliferation of immature cardiomyocytes. We have now examined the hypothesis that suppression of endogenous TGFbeta signaling will boost the proliferative response (DNA synthesis) of cardiac myocytes to serum and/or to the mitogenic factor fibroblast growth factor-2 (FGF-2).

METHODS AND RESULTS

Overexpression of a kinase-deficient TGFbeta type II receptor (TGFbetaRIIDeltaKD) resulted in a 2.8-fold increase in cardiomyocyte DNA synthesis in serum-rich cultures, an effect requiring active FGFR-1 since it was not observed in the presence of excess kinase-deficient FGFR-1. This finding suggested that endogenous TGFbeta-TGFbetaRII suppressed endogenous FGFR-1-mediated signals that stimulate or are permissive for DNA synthesis. TGFbeta had no effect, however, on the FGF-2-induced acute stimulation of extracellular signal regulated kinase1/2. FGF-2, added in the absence or presence of TGFbeta inhibition, elicited a 3- or a 13-fold stimulation of DNA synthesis, respectively, pointing to a synergistic effect.

CONCLUSION

Inhibition of TGFbetaRII-transduced signaling upregulates the proliferative response of cardiomyocytes to serum, and greatly potentiates the stimulatory effect of FGF-2. A combinatorial strategy including activation of FGF-2 and inhibition of TGFbeta-triggered signal transduction may be required for maximal stimulation of immature cardiomyocyte DNA synthesis.

Phosphorylation of serine 262 in the gap junction protein connexin-43 regulates DNA synthesis in cell-cell contact forming cardiomyocytes

Mitogenic stimulation of cardiomyocytes is associated with decreased gap junction coupling and protein kinase C (PKC)-mediated phosphorylation of the gap junction protein connexin43 (Cx43). Identification of and interference with the amino acid(s) that becomes phosphorylated in response to stimulation are important steps towards defining the relationship between Cx43 phosphorylation and cell cycle. Using immunoblotting and phosphospecific antibodies we were able to show that serine-262 (S262) on Cx43 becomes phosphorylated in response to growth factor or PKC stimulation of cardiomyocytes. To examine the effect of Cx43, S262 phosphorylation and cell-cell contact (and/or coupling) on DNA synthesis, we overexpressed wild-type (wt) or mutant Cx43, carrying a S262-to-alanine (S262A, simulating the unphosphorylated state) or a S262-to-aspartate (S262D, simulating constitutive phosphorylation) substitutions in cultures of cell-cell contact forming or isolated cardiomyocytes. Overexpression of wt-Cx43 caused a significant decrease in DNA synthesis irrespective of the presence of cell-cell contact. In cell-cell contact forming cultures, the S262D mutation reversed while the S262A mutation increased the inhibitory effect of Cx43. In the absence of cell-cell contact, the S262-Cx43 mutations had no significant effect on Cx43 inhibition of DNA synthesis. Dye-coupling, evaluated by scrape-loading, indicated increased gap junction permeability in S262A (compared to wt or S262D) overexpressing myocytes. We conclude that Cx43 inhibits cardiomyocyte DNA synthesis irrespectively of cell-cell contact or coupling. Cell-cell contact, and possibly gap junction-mediated communication is required, however, in order to reverse Cx43 inhibition of DNA synthesis by S262 phosphorylation.

Nuclease sensitivity of the human growth hormone-chorionic somatomammotropin locus in pituitary and placenta suggest different mechanisms for tissue-specific regulation

The five human growth hormone (GH) and chorionic somatomammotropin (CS) genes are located at a single locus on chromosome 17. These genes share extensive nucleotide sequence similarity (approximately 94%) even in their flanking DNA, yet GH-N is expressed efficiently in the pituitary under the control of the pituitary-specific factor GHF-1/Pit-1 and the remaining CS-A, CS-B, CS-L and GH-V genes are transcriptionally active in the placenta. Despite this specificity in vivo, a truncated CS-A promoter can bind GHF-1/Pit-1 and allow CS-A promoter activity in pituitary cells in vitro. With a view to assessing whether the placental genes of the GH/CS locus possess a different chromatin structure in the pituitary and are, thus, less transcriptionally active than the GH-N gene, we have compared the DNAase I sensitivity of GH/CS in isolated pituitary and placenta cell nuclei. Our data indicate that these genes are equally sensitive in isolated human pituitary nuclei. By contrast, the CS-A, CS-B and CS-L genes were significantly (P < 0.05) more sensitive than the GH-N gene in isolated human placenta nuclei. Although just not significant, the GH-V gene was slightly more sensitive than the GH-N gene. This pattern was also seen with nuclei from human choriocarcinoma BeWo and JEG-3 cells, which express low and extremely low levels of CS RNA, respectively, but was distinct from the pattern observed in the non placental human cervical carcinoma HeLa cell line. These data indicate that the inactivity of the CS genes in the pituitary does not correlate with a 'closed' chromatin structure. However, they are consistent with a role for a more 'open' chromatin conformation in placenta-specific expression, but not necessarily high levels of transcriptional activity.

Pituitary-specific repression of placental members of the human growth hormone gene family. A possible mechanism for locus regulation

Five members of the human growth hormone (GH) gene family are located at a single locus on chromosome 17. Growth hormone is expressed in the pituitary under the control of the tissue-specific factor Pit 1/GHF-1, and chorionic somatomammotropin (CS) -A, -B, and -L, as well as placental GH variant, are expressed specifically in the placental syncytiotrophoblast. Despite this specificity in vivo, the CS-A promoter can bind Pit 1/GHF-1 and allow CS-A promoter activity in pituitary tumor cells after gene transfer. We have identified and characterized PSF sequences associated with only the placental members in the GH/CS locus which repress placental promoter activity > 90% in transfected pituitary cells. These sequences do not significantly affect promoter function in placental cells after gene transfer. Repressor activity correlates with binding of protein at two sites (PSF-A and PSF-B) with pituitary, but not placental, nuclear extracts. Competition studies suggest an interaction between PSF and Pit 1/GHF-1 proteins. These results indicate that PSF protein can repress CS-A promoter activity in a tissue-specific manner in vitro and provide a possible mechanism by which expression of placental members of the GH family are inhibited in the pituitary in vivo.

Differential expression of human placental growth hormone variant and chorionic somatomammotropin genes in choriocarcinoma cells treated with methotrexate

Chorionic somatomammotropin (hCS) genes (hCS-A and hCS-B) and the placental growth hormone variant (hGH-V) gene are expressed in the syncytiotrophoblast in vivo, and at low levels in cytotrophoblast-like choriocarcinoma (BeWo) cells. Treatment of choriocarcinoma cells with methotrexate (MTX) will induce a cell type intermediate between a cytotrophoblast and syncytiotrophoblast. After treatment with MTX, hCS/hGH-V mRNA levels were decreased in BeWo cells, and only hGH-V and minor hCS-A related transcripts of 1.6, 2.1 and 4.2 kilobases, termed hCS-A2, hCS-A3 and hCS-A4, respectively, were detected. By contrast, chorionic gonadotropin RNA levels were increased. This pattern of hCS/hGH-V expression resembles that observed when BeWo cells are grown in thyroid hormone (T3)-depleted serum, where hGH-V/hCS RNA increases in response to T3. This increase is blunted by MTX treatment, but is not due to a decrease in number or affinity of T3 receptors. These data indicate that the hGH-V and hCS genes can be differentially regulated by MTX, and are consistent with MTX interfering with T3 responsiveness of these genes. Also, if BeWo cells treated with MTX do represent a transitional state, these data raise the possibility that hGH-V and hCS possess a different temporal pattern of expression in the developing trophoblast.

Differential binding of rat pituitary-specific nuclear factors to the 5'-flanking region of pituitary and placental members of the human growth hormone gene family

Placental chorionic somatomammotropin (hCS-A or B) and growth hormone variant (hGH-V) are members of the human growth hormone family, and are related by structure and function to pituitary growth hormone (hGH-N). However, while the hGH-N gene is expressed specifically in the anterior pituitary, hGH-V and hCS are produced in the placenta. Hybrid hGH-N, hGH-V and hCS-A genes containing 5'-flanking sequences, including the endogenous promoter, are preferentially expressed in rat pituitary tumor (GC) cells, after gene transfer. Since interaction with a pituitary-specific protein (Pit 1) is required for efficient hGH-N as well as rat growth hormone (rGH) gene expression in GC cells, binding of pituitary proteins to the hGH-V and hCS-A promoter sequences was investigated. Rat Pit 1 binds at two locations on the hGH-N gene, a distal (-140/-107) and proximal site (-97/-66), in a similar manner to that observed with the rGH gene. By contrast, efficient Pit 1 binding was seen only to the distal site of the hGH-V gene and the proximal site of the hCS-A gene. Although binding of a protein to the distal hCS-A sequences was observed, the site of interaction was truncated (-140/-116), not pituitary-specific, and was more consistent with the binding of Sp1. These data indicate that rat Pit 1 binds to the placental hGH-V and hCS-A genes and correlates with their promoter activity in GC cells after gene transfer.(ABSTRACT TRUNCATED AT 250 WORDS)

Tissue-specific expression and thyroid hormone regulation of the endogenous placental growth hormone variant and chorionic somatomammotropin genes in a human choriocarcinoma cell line

Human (h) placenta-derived choriocarcinoma cell lines (BeWo, JAR, and JEG-3) were examined for expression of pituitary GH (hGH-N) as well as placental GH variant (hGH-V) and chorionic somatomammotropin (hCS, encoded by the hCS-A or hCS-B gene). RNA was isolated and assessed using hGH-N complementary DNA since hGH and hCS genes share more than 90% sequences similarity. The relative expression is BeWo greater than JAR greater than JEG-3. In BeWo cells expression of placental hCS-A, hCS-B, and hGH-V genes, but not pituitary hGH-N, is observed using polyadenylated RNA and oligonucleotide probes specific for the different family members. The absence of hGH-N expression in BeWo cells is not due to deletion or gross rearrangement of the gene. No difference was seen between the hGH/hCS genes in genomic DNA from these cells and the DNA from placenta and pituitary when analyzed by restriction digestion and blotting. Treatment of BeWo cells with 10 nM T3 results in a 6-fold increase in messenger RNA from placental members of the hGH gene family. Levels of hCS-A, hCS-B, and hGH-V transcripts are all elevated. Cellular and secreted proteins from BeWo cells were analyzed by Western blotting, and a band of about 22 kilodaltons was detected using a polyclonal antibody which cross-reacts with hGH-V and hCS. The level of 22 kilodalton band in samples of cellular as well as released protein was increased by T3 treatment. BeWo cells provide a model system for studying hGH-V and hCS regulation as well as tissue-specific expression.

Differential expression of human placental growth-hormone variant and chorionic somatomammotropin in culture

Regulation of human placental growth-hormone variant (hGH-V) in the presence of its own promoter has been studied. At term, 10-20% of placental mRNA is specific for chorionic somatomammotropin (hCS-A and -B) compared with 0.05% hGH-V, yet these genes show more than 90% sequence similarity at the nucleotide level. By using stable gene transfer of intact hGH-V and hCS-A genes into rat pituitary (GC) cells, synthesis and release of hGH-V and hCS are detected. This suggests that hGH-V as well as hCS is secreted during pregnancy. The hCS-A mRNA level is higher than that observed from the hGH-V gene in stably transfected GC cells. Also, a hybrid gene containing hGH-V 5'-flanking DNA was less active than a hybrid hCS-A gene containing equivalent sequences after transient transfection of these cells. This correlates with the binding of a known transcription factor to a proximal region (-97/-66) of the hCS-A promoter, and not the equivalent hGH-V gene sequences. These results indicate that differential expression of hGH-V and hCS in GC cells is related, in part, to the strength of their respective promoters, and suggest a similar mechanism may exist in the placenta.

Human growth hormone gene expression in rat but not human non-pituitary cells after stable gene transfer

Tissue-specific expression of the rat growth hormone (rGH) gene requires binding of a pituitary-specific factor. Binding of this factor has been used to explain tissue-specific expression of the human growth hormone (hGH-N) gene in transfected rat pituitary (GC) tumour cells. Neither rat fibroblast (R2) nor human cervical carcinoma (HeLa) cells contain the rat pituitary-specific factor. Thus, no expression of hGH-N or rGH would be expected in these cells. R2 cell lines containing stably integrated hGH-N or rGH genes were generated. Expression of hGH-N but not rGH was detected. By contrast, stably transfected HeLa cells did not express the endogenous or transfected hGH-N genes. However, an hGH-N transcript was detected when hGH-N gene expression was directed by a viral promoter. This suggests that the block in expression occurs at the level of transcription and not mRNA stability. Hybrid genes containing 496 base pairs (bp) of hGH-N or 234 bp of rGH 5'-flanking DNA, including promoter sequences, fused to the bacterial gene coding for chloramphenicol acetyltransferase were used to stably transfect R2 cells. The hybrid hGH-N gene was more active than a promoterless construction in these cells. By contrast, the hybrid rGH gene was not. These data suggest that the hGH-N gene can be activated by rat transcription factors other than those found in pituitary cells.

The human placental growth hormone variant is mitogenic for rat lymphoma Nb2 cells

Although there is evidence that human (h) placental GH variant (hGH-V) possesses a growth-promoting function, lactogenic activity by the hormone has not been demonstrated. Rat anterior pituitary tumor (GC) cells stably transfected with the hGH-V gene (GC [hGH-V] cells) synthesize and secrete hGH-V. This hormone shares considerable structural similarity with pituitary growth hormone (hGH-N) and chorionic somatomammotropin (hCS) at the nucleotide (greater than 90%) and amino acid (greater than 80%) levels. As expected, both hGH-N and hCS antibodies detect hGH-V by immunoblotting. However, hGH-V, but not hGH-N or hCS, cross-reacts with human or rat pituitary prolactin (PRL) antibodies. These data indicate that structural features shared by hGH-V and pituitary PRL are not present in hGH-N or hCS. Comparison of amino acid sequences implicates two regions that may account for a common epitope between hGH-V and hPRL, and structural difference from hGH-N and hCS. The possible lactogenic activity by hGH-V was assessed in a rat lymphoma Nb2 cell bioassay. Conditioned medium from GC[hGH-V] cells permitted growth of lactogen-dependent Nb2 lymphoma cells in culture. This activity was blocked by antibodies raised to rat PRL but not hPRL or hGH-N. Comparison of the hGH-V amino acid sequence with those from 14 other lactogenic hormones, including hPRL, hCS and hGH-N, reveals 6 conserved amino acids. These data indicate a lactogenic as well as growth-promoting function for the secreted hGH-V protein in vivo.

Human chorionic somatomammotropin and growth hormone gene expression in rat pituitary tumour cells is dependent on proximal promoter sequences

Human placental chorionic somatomammotropin (hCS-A or hCS-B) and pituitary growth hormone (hGH-N) are related by structure and function. The hCS-A gene is expressed in rat pituitary tumour (GC) cells after gene transfer. Deletion of hCS-A 5'-flanking DNA reveals repressor activity upstream of nucleotide -132, and a region essential for expression in GC cells between nucleotides -94 and -61. The sequences in this region differ from the equivalent hGH-N gene DNA by one nucleotide, and include the binding site (-92 to -65) for a pituitary-specific factor (GHF-1), required for hGH-N expression in GC cells. Exchange of hGH-N with hCS-A gene DNA in this region maintains expression in GC cells. By contrast, modification of these sequences blocks expression. These data indicate that proximal promoter sequences, equivalent to those bound by GHF-1 on the hGH-N gene, are required for hCS-A expression in GC cells.

Ubiquitinated histone H2B is preferentially located in transcriptionally active chromatin

Using an anti-ubiquitin antibody in Western blotting experiments, we detected polyubiquitinated species of histones H2A, H2A.Z, and H2B in histone preparations of bovine thymus, chicken erythrocyte, and Tetrahymena macro- and micronuclei. Histone H2A had the greatest level of polyubiquitinated species, with tetra- to hexaubiquitinated forms of this histone being observed. The fraction of bovine thymus and chicken erythrocyte chromatin enriched in transcriptionally active gene sequences was enriched in mono- and polyubiquitinated species of histones H2A, H2B, and H2A.Z, especially in the ubiquitinated forms of histone H2B. Histones H2A and H2B were ubiquitinated in the transcriptionally active Tetrahymena macronucleus, with monoubiquitinated (u) H2B being the predominant ubiquitinated histone species. Ubiquitinated forms of histones H2A and H2B were found in transcriptionally inert micronuclei, but at lower levels than seen in macronuclear histones. Also, the level of micronuclear uH2A was greater than that of uH2B which may be from macronuclei that contaminate the preparation. These results indicate that the mono- and polyubiquitinated species of histone H2B are preferentially located in transcriptionally active chromatin regions. Ubiquitinated histone H2A is located in both expressed and repressed chromatin domains, but expressed chromatin is enriched in mono- and polyubiquitinated forms of this histone. These observations are consistent with the hypothesis that ubiquitinated histones have a role maintaining the structure of transcriptionally active chromatin.

Structure of polyubiquitinated histone H2A

We have recently demonstrated that trout liver histones H2A, H2B, and H2A.Z can be polyubiquitinated [Davie, J.R., Delcuve, G.P., Nickel, B.E., Moyer, R., & Bailey, G. (1987) Cancer Res. 47, 5407-5410]. In the present study we determined the arrangement of the ubiquitin molecules in polyubiquitinated histone H2A. Trout liver chromatin fragments. which had histone H1 removed, were digested with Staphylococcus aureus (V8 strain) protease which cleaves specifically on the carboxyl side of glutamic acid residues under the conditions used. The V8 protease readily degraded histone H2A and ubiquitinated (u) H2A at equivalent rates. One site in H2A and uH2A, the peptide bond between Glu 121 and Lys 122, was cleaved, yielding protein species cH2A and cuH2A, respectively. None of the other nucleosomal histones (H2B, H2A.Z, H3, and H4) including uH2B and uH2A.Z were sensitive to digestion. Trout liver histones cleaved with either V8 protease, histone H2A specific protease, or cyanogen bromide were resolved by two-dimensional gel electrophoresis and ubiquitinated peptides detected with anti-ubiquitin IgG. The results suggest that the major arrangement of ubiquitin in polyubiquitinated H2A is a chain of ubiquitin molecules joined to each other by isopeptide bonds to a ubiquitin molecule that is attached to the epsilon-amino group of lysine 119 of histone H2A.

The protamine gene chromatin in developing trout testis exists in an altered state

Micrococcal nuclease was used to probe the nucleosomal organization of the rainbow trout germ-line-specific protamine multi-gene family in testis and erythrocytes. In erythrocyte chromatin, the repressed protamine genes show a distinct nucleosomal repeat pattern. However, in early-stage testis chromatin, where the protamine genes are expressed, they lack a distinct nucleosomal repeat pattern, indicating that the disrupted chromatin structure is related to their transcriptional activity. Micrococcal nuclease-digested testis and erythrocyte chromatin was separated into soluble and insoluble fractions. Transcriptionally active/competent genes of testis that had been labeled by nuclear nick-translation were enriched in the low-salt eluted, micrococcal nuclease-sensitive chromatin fraction. This fraction was not enriched in protamine DNA sequences. In testis, but not erythrocytes, protamine DNA sequences were slightly enriched in chromatin that fractionated with insoluble nuclear material, suggesting that transcriptionally active protamine gene chromatin has an insoluble character. Since the different protamine genes may not be simultaneously expressed, our results show the distribution of both transcriptionally active and inactive protamine genes. However, our observations indicate that the active germ-line-specific protamine gene chromatin shares several, but not all, of the features associated with other active tissue-specific genes.

Reduced levels of histones H1o and H1b, and unaltered content of methylated DNA in rainbow trout hepatocellular carcinoma chromatin

The levels of histone subtypes and DNA methylation of aflatoxin-induced rainbow trout hepatocellular carcinoma and adult liver nuclei were compared. The hepatocellular carcinoma nuclei were enriched in the ubiquitinated species of histone H2A and depleted in histones H1o and H1b. The 5-methylcytosine content and methylation patterns of the vitellogenin genes and the transcriptionally inactive TPG-3 protamine gene were not altered in the trout hepatocellular carcinoma DNA. Thus, undermethylation of DNA is not a general feature of chemically induced tumors in vivo.

The ubiquitinated histone species are enriched in histone H1-depleted chromatin regions

Bovine thymus and trout testis chromatin were fractionated into regions which differed in their micrococcal nuclease accessibility and solubility properties, and the distribution of the ubiquitinated histone species among these chromatin regions was elucidated. Ubiquitinated (u) species of histones H2A and H2B were enriched in the nuclease-sensitive, low-ionic-strength, soluble fraction of both chromatins. These results indicate that the presence of ubiquitinated histones may alter nucleosome-nucleosome interactions and destabilize higher-order chromatin structures. Bovine thymus chromatin was separated into aggregation-resistant, salt-soluble and aggregation-prone, salt-insoluble chromatin fractions. The aggregation-resistant chromatin fraction depleted in H1 histones was enriched in uH2A and uH2B, with uH2B showing the greater enrichment. The chromatin fragments were also stripped and reconstituted with the H1 histones prior to fractionation. The results were the same as above: uH2A and uH2B were preferentially localized in the aggregation-resistant. H1-depleted chromatin fraction, suggesting that chromatin regions enriched in ubiquitinated histone species have a reduced affinity for the H1 histones. Thus, ubiquitinated histone species may be one of the contributing factors in the differential assembly of various parts of the genome.

Changes in the histone H2A variant H2A.Z and polyubiquitinated histone species in developing trout testis

The trout histone H2A variant H2A.Z has been identified by its electrophoretic mobility on two-dimensional polyacrylamide gels and its N-terminal amino acid sequence. Similar to bovine H2A.Z and chicken H2A.F (also called H2A.Z and M1), the trout H2A.Z had a two-residue extension when aligned with trout H2A and a 67% sequence homology with the N-terminal portion of trout H2A. The first 29 amino acids of trout H2A.Z were identical with those of chicken H2A.F and differed from those of bovine H2A.Z at only one position. Thus, the N-terminal part of histone H2A.Z appears to be highly conserved. The levels of histone H2A.Z and ubiquitinated species of the histones H2A, H2A.Z, and H2B, which were detected with an anti-ubiquitin antibody, were studied at various stages of trout testis development. At the final stages of spermatogenesis in trout, histones are replaced by protamines. Ubiquitinated and diubiquitinated histone H2A remained at similar levels in early and late stage testis nucleohistone. In the late stage testis chromatin (nucleohistone), ubiquitinated histone H2A.Z was not detected, the level of ubiquitinated histone H2B was reduced, and the amount of diubiquitinated histone H2B increased. There was also a marked reduction in the level of histone H2A.Z. This observation suggests nucleosomes with this histone variant were selectively disassembled during the transition from nucleohistone to nucleoprotamine, indicating that protamine deposition is not a random process in rainbow trout.

Brief clinical report: ring chromosome 17 in a mentally retarded young man - clinical, cytogenetic, and biochemical investigations

A young, mentally retarded man with seizures was discovered to have a ring chromosome 17. He had no major anomalies. The phenotype associated with r(17) probably is variable. The patient's deletion and genotype allowed us to reduce further the chromosome location of the acid alpha-glucosidase gene.

Extension of human acid alpha-glucosidase polymorphism by isoelectric focusing in polyacrylamide gel

1. A method to analyse acid alpha-glucosidase (GAA) activity in human tissues by flatbed polyacrylamide gel isoelectric focusing has been devised. 2. With this method the GAA polymorphism has been extended from three to six commonly occurring phenotypes. 3. After isoelectric focusing the GAA2 isozyme migrated cathodally with respect to the GAA1 isozyme, whereas with the previous starch-gel electrophoresis method their relative positions were reversed. 4. The six common phenotypes are generated by three alleles, GAA*1, GAA*2 and GAA*4 with frequencies of 0.91, 0.03 and 0.06, respectively.