Inhibition of MALT1 and BCL2 induces synergistic anti-tumor activity in models of B cell lymphoma

The activated B cell (ABC) subset of diffuse large B cell lymphoma (DLBCL) is characterized by chronic B cell receptor signaling and associated with poor outcomes when treated with standard therapy. In ABC-DLBCL, MALT1 is a core enzyme that is constitutively activated by stimulation of the B cell receptor or gain-of-function mutations in upstream components of the signaling pathway, making it an attractive therapeutic target. We discovered a novel small molecule inhibitor, ABBV-MALT1, that potently shuts down B cell signaling selectively in ABC-DLBCL preclinical models leading to potent cell growth and xenograft inhibition. We also identified a rational combination partner for ABBV-MALT1 in the BCL2 inhibitor, venetoclax, which when combined significantly synergizes to elicit deep and durable responses in preclinical models. This work highlights the potential of ABBV-MALT1 monotherapy and combination with venetoclax as effective treatment options for patients with ABC-DLBCL.

Genes Involved in Maintaining Mitochondrial Membrane Potential Upon Electron Transport Chain Disruption

Mitochondria are biosynthetic, bioenergetic, and signaling organelles with a critical role in cellular physiology. Dysfunctional mitochondria are associated with aging and underlie the cause of a wide range of diseases, from neurodegeneration to cancer. Through signaling, mitochondria regulate diverse biological outcomes. The maintenance of the mitochondrial membrane potential, for instance, is essential for proliferation, the release of mitochondrial reactive oxygen species, and oxygen sensing. The loss of mitochondrial membrane potential triggers pathways to clear damaged mitochondria and often results in cell death. In this study, we conducted a genome-wide positive selection CRISPR screen using a combination of mitochondrial inhibitors to uncover genes involved in sustaining a mitochondrial membrane potential, and therefore avoid cell death when the electron transport chain is impaired. Our screen identified genes involved in mitochondrial protein translation and ATP synthesis as essential for the induction of cell death when cells lose their mitochondrial membrane potential. This report intends to provide potential targets for the treatment of diseases associated with mitochondrial dysfunction.

Loss of growth factor receptor signaling in the oral mucosa during primary SIV infection may enhance apoptosis and promote pathogenesis

BACKGROUND

The development of susceptibility to secondary pathogenic infections in the oral cavity during HIV infection is likely to result from or coincide with deterioration of the local mucosal immune system.

METHODS

We have utilized the SIV model to investigate the kinetics and magnitude of oral pathogenesis during systemic dissemination of intravenously inoculated SIVmac251.

RESULTS

Viral replication was detected in oropharyngeal lymph nodes at 6 weeks post-infection and shown to be coincident with a broad scale loss of growth factor receptor transcription in the oral mucosa, providing multiple avenues for blocking the normal activity of apoptosis inhibitors that function through Bcl2- and p53-dependent pathways.

CONCLUSIONS

Our findings suggest that the normal balance between cell death and regeneration may be rapidly disrupted in the oral mucosa during the early stages of immunodeficiency virus infection, setting the stage for continuing deterioration of immune function and the development of susceptibility to secondary infections.

Pegylated interferon-alpha 2a treatment of chronic SIV-infected macaques

BACKGROUND

In vitro and clinical observations in HIV-infected patients receiving interferon alpha therapy have shown a reduction in HIV loads. Limited investigations have explored the innate or adaptive immune responses of IFN-alpha on SIV replication in vivo.

METHODS

Seven chronically infected rhesus macaques were given pegylated IFN-alpha 2a (n = four) or saline (n = three) injections once weekly for 14 weeks. Weekly peripheral blood samples were taken for safety parameters, viral load determinations, and measurements of innate and adaptive immune responses.

RESULTS

Pharmacokinetic measurements demonstrated therapeutic peg-IFN-alpha levels for the initial period of therapy and IFN-alpha inducible antiviral molecules were increased sporadically in the PBMC mRNA of the treatment group. Despite the demonstrable effect of the IFN-alpha injections, the treatment had no effect on plasma viral RNA levels.

CONCLUSIONS

This work demonstrates that while short term IFN-alpha therapy induces innate antiviral immunity, it does not dramatically enhance or suppress viral replication. However, studies in the SIV model to determine therapeutic potential of chronic IFN-alpha therapy for the treatment of HIV will require macaque specific cytokines.

Long-term results of a hydroxyapatite-coated femoral component in total hip replacement: a 15- to 21-year follow-up study

Between 1986 and 1991 we implanted 331 consecutive Furlong hydroxyapatite-coated femoral components of a total hip replacement in 291 patients. A cemented acetabular prosthesis was used in 217 hips and a hydroxyapatite-coated component in 114. We describe the long-term clinical and radiological survival of the femoral component at a mean follow-up of 17.5 years (15 to 21). Only two patients (0.68%) were lost to follow-up. With revision of the femoral component for any reason as the endpoint, the survival at a mean of 17 years was 97.4% (95% confidence interval 94.1 to 99.5), and with revision for aseptic loosening as the endpoint it was 100%. The survival at a maximum of 21 years with revision of the femoral component for any reason as the endpoint was 97.4% (95% confidence interval 81.0 or 99.5). These results compare favourably with the best long-term results of cemented or uncemented femoral components used in total hip replacement.

Gene expression profiling of gut mucosa and mesenteric lymph nodes in simian immunodeficiency virus-infected macaques with divergent disease course

BACKGROUND

Although the majority of drug-naïve HIV-infected patients develop acquired immunodeficiency syndrome (AIDS), a small percentage remains asymptomatic without therapeutic intervention.

METHODS

We have utilized the simian immunodeficiency virus (SIV)-infected rhesus macaque model to gain insights into the molecular mechanisms of long-term protection against simian AIDS.

RESULTS

Chronically SIV-infected macaques with disease progression had high viral loads and CD4(+) T-cell depletion in mucosal tissue and peripheral blood. These animals displayed pathologic changes in gut-associated lymphoid tissue (GALT) and mesenteric lymph node that coincided with increased expression of genes associated with interferon induction, inflammation and immune activation. In contrast, the animal with long-term asymptomatic infection suppressed viral replication and maintained CD4(+) T cells in both GALT and peripheral blood while decreasing expression of genes involved in inflammation and immune activation.

CONCLUSIONS

Our findings suggest that reduced immune activation and effective repair and regeneration of mucosal tissues correlate with long-term survival in SIV-infected macaques.

Cemented revision total hip arthroplasty with impaction bone grafting in Gaucher's disease

Total hip arthroplasty in Gaucher's disease has been associated with high rates of loosening after all types of arthroplasty. We present a patient with type 1 Gaucher's disease who underwent revision cemented total hip arthroplasty for aseptic loosening after 12 months of enzyme replacement therapy. Major osteolysis was managed by impaction morcellized bone grafting. An excellent clinical and radiographic result was obtained at 5-year follow-up. Enzyme replacement therapy combined with modern revision techniques may offer improved outcomes for patients with Gaucher's disease.

Cvt18/Gsa12 is required for cytoplasm-to-vacuole transport, pexophagy, and autophagy in Saccharomyces cerevisiae and Pichia pastoris

Eukaryotic cells have the ability to degrade proteins and organelles by selective and nonselective modes of micro- and macroautophagy. In addition, there exist both constitutive and regulated forms of autophagy. For example, pexophagy is a selective process for the regulated degradation of peroxisomes by autophagy. Our studies have shown that the differing pathways of autophagy have many molecular events in common. In this article, we have identified a new member in the family of autophagy genes. GSA12 in Pichia pastoris and its Saccharomyces cerevisiae counterpart, CVT18, encode a soluble protein with two WD40 domains. We have shown that these proteins are required for pexophagy and autophagy in P. pastoris and the Cvt pathway, autophagy, and pexophagy in S. cerevisiae. In P. pastoris, Gsa12 appears to be required for an early event in pexophagy. That is, the involution of the vacuole or extension of vacuole arms to engulf the peroxisomes does not occur in the gsa12 mutant. Consistent with its role in vacuole engulfment, we have found that this cytosolic protein is also localized to the vacuole surface. Similarly, Cvt18 displays a subcellular localization that distinguishes it from the characterized proteins required for cytoplasm-to-vacuole delivery pathways.

Cis-polyunsaturated fatty acids stimulate beta1 integrin-mediated adhesion of human breast carcinoma cells to type IV collagen by activating protein kinases C-epsilon and -mu

We have investigated the effects of various fatty acids (FAs) on integrin-mediated MDA-MB-435 breast carcinoma cell adhesion to type IV collagen (collagen IV) in vitro. Arachidonic acid (AA) and linoleic acid both induced a dose-dependent increase in cell adhesion to collagen IV with no significant increase in nonspecific adhesion to polylysine and BSA. Oleic acid (a monounsaturated FA), AA methyl ester, and linoelaidic acid (a trans-isomer of linoleic acid) failed to stimulate adhesion to collagen IV, suggesting that these effects required cis-polyunsaturation and a free carboxylic moiety and that they were not due to membrane perturbations. Calphostin C, a protein kinase C (PKC) inhibitor, blocked cis-polyunsaturated FA (cis-PUFA)-induced cell adhesion in a dose-dependent manner, suggesting a role for a calcium-dependent PKC in this signal transduction pathway. Immunoblotting revealed that cis-PUFAs induced the translocation of PKCepsilon and PKCmu, two of the novel PKC isozymes, from the cytosol to the membrane. In contrast, a conventional PKC isozyme, PKCalpha, as well as the atypical isozymes, PKCzeta and PKCiota, did not translocate after cis-PUFA treatment. Function-blocking antibodies specific for alpha1, alpha2, and beta1, integrin subunits inhibited cell adhesion to collagen IV, whereas antibodies to alpha3 and alpha5 did not. No increase in the expression of these integrins on the cell surface was detected after the incubation of cells with cis-PUFAs, suggesting that there is an increase in the activity, but not in the amount, of these beta1, integrins. Altogether, these data suggest that cis-PUFAs enhance human breast cancer cell adhesion to collagen IV by selectively activating specific PKC isozymes, which leads to the activation of beta1 integrins.

Increased marine production of N2O due to intensifying anoxia on the Indian continental shelf

Eutrophication of surface waters and hypoxia in bottom waters has been increasing in many coastal areas, leading to very large depletions of marine life in the affected regions. These areas of high surface productivity and low bottom-water oxygen concentration are caused by increasing runoff of nutrients from land. Although the local ecological and socio-economic effects have received much attention, the potential contribution of increasing hypoxia to global-change phenomena is unknown. Here we report the intensification of one of the largest low-oxygen zones in the ocean, which develops naturally over the western Indian continental shelf during late summer and autumn. We also report the highest accumulations yet observed of hydrogen sulphide (H2S) and nitrous oxide (N2O) in open coastal waters. Increased N2O production is probably caused by the addition of anthropogenic nitrate and its subsequent denitrification, which is favoured by hypoxic conditions. We suggest that a global expansion of hypoxic zones may lead to an increase in marine production and emission of N2O, which, as a potent greenhouse gas, could contribute significantly to the accumulation of radiatively active trace gases in the atmosphere.

Apg5p functions in the sequestration step in the cytoplasm-to-vacuole targeting and macroautophagy pathways

The cytoplasm-to-vacuole targeting (Cvt) pathway and macroautophagy are dynamic events involving the rearrangement of membrane to form a sequestering vesicle in the cytosol, which subsequently delivers its cargo to the vacuole. This process requires the concerted action of various proteins, including Apg5p. Recently, it was shown that another protein required for the import of aminopeptidase I (API) and autophagy, Apg12p, is covalently attached to Apg5p through the action of an E1-like enzyme, Apg7p. We have undertaken an analysis of Apg5p function to gain a better understanding of the role of this novel nonubiquitin conjugation reaction in these import pathways. We have generated the first temperature-sensitive mutant in the Cvt pathway, designated apg5(ts). Biochemical analysis of API import in the apg5(ts) strain confirmed that Apg5p is directly required for the import of API via the Cvt pathway. By analyzing the stage of API import that is blocked in the apg5(ts) mutant, we have determined that Apg5p is involved in the sequestration step and is required for vesicle formation and/or completion.

Swainsonine protects both murine and human haematopoietic systems from chemotherapeutic toxicity

The haematopoietic system is sensitive to cytotoxic damage and is often the site of dose-limiting toxicity. We previously reported that swainsonine, an inhibitor of protein glycosylation, reduced the bone marrow toxicity resulting from a single dose of anticancer drugs in otherwise healthy mice. However, more important questions are (1) can swainsonine protect tumour-bearing mice without interfering with the anti-tumour effects of the drugs, and (2) can swainsonine stimulate haematopoietic activity of human, as well as murine, bone marrow. We demonstrate here that swainsonine protects C57BL/6 mice bearing melanoma-derived tumours from cyclophosphamide-induced toxicity without interfering with the drug's ability to inhibit tumour growth. Similar results were obtained in vivo with 3'-azido-3'-deoxythymidine (AZT), a myelosuppressive agent often used in therapy for acquired immune deficiency syndrome. Swainsonine increased both total bone marrow cellularity and the number of circulating white blood cells in mice treated with doses of AZT that typically lead to severe myelosuppression. Swainsonine also increased the number of erythroid and myeloid colony forming cells (CFCs) in short-term cultures of murine bone marrow, restoring the number of progenitor cells to the control level in the presence of AZT doses that reduced CFCs by 80%. With respect to the sensitivity of human haematopoietic cells to swainsonine, we show that swainsonine protected human myeloid progenitor cells from AZT toxicity in vitro. These results suggest that swainsonine may be useful as an adjuvant in several types of human chemotherapy.

A protein conjugation system essential for autophagy

Autophagy is a process for the bulk degradation of proteins, in which cytoplasmic components of the cell are enclosed by double-membrane structures known as autophagosomes for delivery to lysosomes or vacuoles for degradation. This process is crucial for survival during starvation and cell differentiation. No molecules have been identified that are involved in autophagy in higher eukaryotes. We have isolated 14 autophagy-defective (apg) mutants of the yeast Saccharomyces cerevisiae and examined the autophagic process at the molecular level. We show here that a unique covalent-modification system is essential for autophagy to occur. The carboxy-terminal glycine residue of Apg12, a 186-amino-acid protein, is conjugated to a lysine at residue 149 of Apg5, a 294-amino-acid protein. Of the apg mutants, we found that apg7 and apg10 were unable to form an Apg5/Apg12 conjugate. By cloning APG7, we discovered that Apg7 is a ubiquitin-E1-like enzyme. This conjugation can be reconstituted in vitro and depends on ATP. To our knowledge, this is the first report of a protein unrelated to ubiquitin that uses a ubiquitination-like conjugation system. Furthermore, Apg5 and Apg12 have mammalian homologues, suggesting that this new modification system is conserved from yeast to mammalian cells.

The role of protein glycosylation inhibitors in the prevention of metastasis and therapy of cancer

Oligosaccharide moieties of cell-surface glycoproteins are thought to be involved in recognition events during cancer metastasis and invasion. Swainsonine, an inhibitor of the Golgi alpha-mannosidase II, has been shown to block pulmonary colonization by tumor cells and stimulate components of the immune system. Swainsonine also abrogates much of the toxicity of chemotherapeutic agents and stimulates bone marrow hematopoietic progenitor cells, suggesting additional therapeutic applications. We are currently characterizing the ability of swainsonine to modify cell growth in human and murine bone marrow progenitor cells. Furthermore, we are examining crucial steps in metastasis that depend upon cell surface molecules that play a role in cell-matrix interactions. Our work shows that tumor cell adhesion to collagen IV in vitro is rapidly stimulated by cis-polyunsaturated fatty acids and is dependent on protein kinase C activity. We are investigating the hypothesis that integrins are critical components of this adhesion and are examining potential signal transduction pathways that lead to the modulation of cell adhesion.

Expression of cornifin in squamous differentiating epithelial tissues, including psoriatic and retinoic acid-treated skin

The expression of cornifin, a putative cross-linked envelope precursor, was investigated in several squamous differentiating tissues by in situ hybridization and immunohistochemical analysis. Cornifin mRNA and protein, which are absent in the normal mucociliary tracheal epithelium, are induced in the suprabasal layers of the squamous metaplastic tracheal epithelium of vitamin A-deficient hamsters. Similar to the induction of squamous metaplasia in vivo, culture of rabbit tracheal cells in the absence of retinoids results in squamous differentiation and expression of cornifin. This induction of cornifin expression is suppressed by retinoic acid and several of its analogs. Cornifin mRNA and protein are also detected in the suprabasal layers of the squamous epithelium of rabbit esophagus and tongue. The distribution of cornifin in human epidermis was compared with that of two other crosslinked envelope precursor proteins, involucrin and loricrin. The localization of cornifin and involucrin is very similar. Both are induced in the spinous layer and appear at an earlier stage during epidermal differentiation than loricrin. The expression of cornifin is greatly increased in psoriatic skin. Cornifin mRNA is barely detectable in normal epidermis, whereas it is present at relatively high levels in the suprabasal layers of psoriatic epidermis. Topical treatment with RA results in thickening of the skin and increases the level of cornifin mRNA and protein in the upper spinous layers of mouse skin. Cornifin expression correlates generally with squamous differentiation in a variety of tissues and is abnormally regulated in psoriatic skin and in skin treated topically with retinoic acid.

Cornifin, a cross-linked envelope precursor in keratinocytes that is down-regulated by retinoids

In this study, we have characterized the cDNA clone SQ37 that was isolated previously from a rabbit squamous cell library. The gene encodes a 14-kDa protein that appears to function as a component of the cross-linked envelope in squamous differentiating cells. The protein, which has been named cornifin, has a high content of proline (31%), glutamine (20%), and cysteine (11%) and contains 13 repeats of an octapeptide (consensus sequence, EPCQPKVP) at its C terminus. SQ37 mRNA and protein are induced during squamous differentiation of rabbit tracheal (RbTE) cells and human epidermal keratinocytes. This induction is repressed by retinoids. Immunohistochemical studies reveal SQ37 immunoreactivity in fragmented cross-linked envelopes from squamous-differentiated RbTE cells and in the suprabasal layers of the epidermis. In situ hybridization analysis showed that the presence of SQ37 mRNA is restricted to the suprabasal layers. Treatment of RbTE cells with a Ca2+ ionophore induces cross-linking of the SQ37 protein into higher molecular weight complexes. This cross-linking reaction appears to be mediated by transglutaminase type I. Our observations suggest that the protein encoded by SQ37 participates in the assembly of the cross-linked envelope.

Regulation of type I and type II transglutaminase in normal human bronchial epithelial and lung carcinoma cells

In cultured, undifferentiated normal human bronchial epithelial (HBE) cells, transglutaminase activity was localized predominantly in the cytosolic fraction of cell lysates. Upon squamous differentiation, this cytosolic activity declined and was replaced by a 40-fold increase in the activity of particulate (membrane-associated) transglutaminase. Immunoblot analysis demonstrated that the cytosolic transglutaminase was Type II (tissue) transglutaminase and that squamous differentiation shifted gene expression to the Type I (epidermal) transglutaminase. Retinoic acid, an inhibitor of squamous cell differentiation, suppressed the increase in Type I transglutaminase. The decrease in Type II transglutaminase activity was unaffected by retinoic acid. Transforming growth factor-beta 1 (TGF-beta 1) enhanced Type II transglutaminase activity about 10-fold in the undifferentiated cells but did not increase Type I transglutaminase or cholesterol sulfate, two early markers of squamous differentiation. TGF-beta 2 was equivalent to TGF-beta 1 in inducing Type II transglutaminase and in inhibiting the growth of HBE cells. The differentiation-related and TGF-beta-induced changes in transglutaminase activity were reflected in the level of transglutaminase Type I and Type II protein and mRNA. Expression of transglutaminases in lung carcinoma cell lines was variable. No correlation was observed between the expression of Type I transglutaminase and the classification of the cells as squamous cell carcinoma. Several lung carcinoma cell lines exhibited high levels of Type II transglutaminase activity that were increased several-fold by TGF-beta 1 treatment. Retinoic acid was ineffective in altering transglutaminase expression in most cell lines but induced Type II transglutaminase in a time- and dose-dependent manner in NCI-HUT-460 cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Retinoic acid receptors as regulators of human epidermal keratinocyte differentiation

To examine the role of nuclear retinoic acid (RA) receptors (RARs) in the regulation of squamous differentiation in normal human epidermal keratinocytes (NHEK), we analyzed binding activity, mRNA expression, and transcriptional activity of the endogenously expressed RARs. Specific RA-binding activity eluted from size-exclusion HPLC with an apparent mol wt of 50 kilodaltons and was predominantly (greater than 95%) associated with the NHEK nuclear cell fraction. This RAR-binding activity represented in part the expression of RAR alpha and RAR gamma genes, whose transcripts were expressed in similar abundance in undifferentiated NHEK. Differentiation resulted in lower mRNA expression of RAR alpha relative to the mRNA expression of RAR gamma. Treatment of NHEK cells with 10(-6) M RA did not induce expression of RAR beta mRNA. Similarly, three squamous cell carcinoma cell lines derived from human skin and oral cavity expressed RAR alpha and RAR gamma transcripts, but not RAR beta transcripts. Transfection of NHEK with chloramphenicol acetyltransferase (CAT) reporter plasmids indicated that the endogenously expressed RARs could activate transcription through the RAR beta response element in a concentration-dependent manner with doses of 10(-9) M RA and higher. CAT expression was not activated through TRE, a palindromic thyroid hormone response element with purported RA responsiveness. The competitive binding of benzoic acid derivatives of RA to RAR correlated with the ability of each analog to suppress mRNA expression of the squamous cell markers, involucrin, type I transglutaminase, and SQ37, and to activate transcription of the RAR beta response element-CAT reporter. These results demonstrate that the control of NHEK differentiation by RA is consistent with the interaction of the retinoid with RAR and the regulation of transcription by that ligand-receptor complex.

Identification of a new squamous cell differentiation marker and its suppression by retinoids

Rabbit tracheobronchial epithelial cells (RbTE) can undergo squamous cell differentiation under defined culture conditions and, therefore, have been used as a model to study the regulation of squamous cell differentiation markers. In the present study, we identified a 20-kDa protein, designated rSQ20, in the serum-free growth medium conditioned by RbTE cells undergoing squamous cell differentiation. The protein was also found in extracts of squamous differentiated cells. rSQ20 was labeled by cells incubated with [35S]methionine but not with [3H]glucosamine, suggesting that it is not a glycoprotein. Undifferentiated cells did not produce this protein. rSQ20 was detected in the conditioned medium of RbTE cells after they reached a confluent and growth-arrested state, and thereafter its level increased markedly and concurrently with an increase in type I (epidermal) transglutaminase, an established marker of squamous cell differentiation. rSQ20 found in concentrated conditioned medium of squamous differentiated RbTE cells was eluted from a gel filtration column as a protein of 20 kDa, similar to that found by gel electrophoresis under denaturing conditions, suggesting that it is not a multimeric protein. A protein with an apparent molecular weight of 16 kDa (rSQ16), probably the product of partial proteolysis of rSQ20, was often found in various amounts in the conditioned medium of differentiated RbTE cells. beta-All-trans retinoic acid and other vitamin A analogues (retinoids), which suppress squamous cell differentiation, inhibited the expression of rSQ20 in RbTE cells. RbTE cells immortalized by transfection with SV40 large T antigen as well as malignantly transformed derivatives obtained from the immortalized cells by further transfection with v-Ha-ras secreted SQ20 and SQ16 when grown to high cell densities although their squamous differentiation was impaired. An analogous protein with an apparent molecular weight of 16 kDa, designated hSQ16, was detected in the medium of differentiated normal human bronchial epithelial (NHBE) cells and normal human epidermal keratinocytes (NHEK). No such protein could be detected in the medium in which undifferentiated NHBE or NHEK cells were grown. These results suggest that rSQ20 and hSQ16 are new markers of squamous cell differentiation.

Expression of nuclear retinoic acid receptors in normal tracheobronchial cells and in lung carcinoma cells

Retinoids are important regulators of the growth and differentiation of tracheobronchial epithelial cells. To determine the mechanism of action of retinoids in these cells, we began to examine the expression of nuclear retinoic acid receptors (RARs) in normal human and rabbit tracheobronchial epithelial (HBE and RbTE, respectively) cells and in several lung carcinoma cell lines. A specific nuclear RAR-binding activity with a molecular weight of 50,000 was identified in these cells. A correlation was found between the binding of several retinoids to this RAR and their ability to inhibit transglutaminase Type I activity. Normal HBE and RbTE cells contained two RAR alpha mRNA transcripts, 2.6 and 3.5 kb in size, and one 3.1 kb RAR gamma transcript. RAR beta transcripts were undetectable in HBE cells. RAR expression was unchanged during squamous differentiation. Treatment of HBE and RbTE cells with 100 nM retinoic acid increased RAR beta mRNA expression but did not change the levels of RAR alpha and RAR gamma. In contrast, retinoic acid suppressed in these cells the level of involucrin, transglutaminase Type I, and SQ37 mRNA. In comparison with normal HBE cells, certain lung carcinoma cell lines appear to have an altered expression of RAR beta and RAR gamma. Human bronchial fibroblasts (HBF) expressed RAR alpha and RAR gamma transcripts of the same size as HBE cells. HBF cells contain low levels of a 2.9- and 3.3-kb RAR beta mRNA. Treatment of HBF cells with retinoic acid increased the level of RAR beta mRNA in a time-dependent manner; the maximal induction was about 15-fold. On the basis of these findings we hypothesize that RARs are involved in the suppression of squamous differentiation in tracheobronchial epithelial cells and that lung fibroblasts are target cells for retinoids.

Induction of extracellular matrix gene expression in normal human keratinocytes by transforming growth factor beta is altered by cellular differentiation

Changes in epithelial substrate have been related to the cellular capacity for proliferation and to changes in cellular behavior. The effect of TGF beta 1 on the expression of the basement membrane genes, fibronectin, laminin B1, and collagen alpha 1 (IV), was examined. Northern analysis revealed that treatment of normal human epidermal keratinocytes with 100 pM TGF beta 1 increased the expression of each extracellular matrix (ECM) gene within 4 h of treatment. Maximal induction was reached within 24 h after treatment. The induction of ECM mRNA expression was dose dependent and was observed at doses as low as 1-3 pM TGF beta 1. Incremental doses of TGF beta 1 also increased cellular levels of fibronectin protein in undifferentiated keratinocytes and resulted in increased secretion of fibronectin. Squamous-differentiated cultures of keratinocytes expressed lower levels of the extracellular matrix RNAs than did undifferentiated cells. Treatment of these differentiated cells with TGF beta 1 induced the expression of fibronectin mRNA to levels seen in TGF beta-treated, undifferentiated keratinocytes but only marginally increased the expression of collagen alpha 1 (IV) and laminin B1 mRNA. The increased fibronectin mRNA expression in the differentiated keratinocytes was also reflected by increased accumulation of cellular and secreted fibronectin protein. The inclusion of cycloheximide in the protocol indicated that TGF beta induction of collagen alpha 1 (IV) mRNA was signaled by proteins already present in the cells but that TGF beta required the synthesis of a protein(s) to fully induce expression of fibronectin and laminin B1 mRNA. The differential regulation of these genes in differentiated cells may be important to TGF beta action in regulating reepithelialization.

Positive and negative regulation of proliferation and differentiation in tracheobronchial epithelial cells

The lung (in particular the bronchial epithelium) is a major site for tumor formation in humans. Environmental factors in conjunction with genetic factors are important determinants in this disease. The acquisition of defects in the control of proliferation and differentiation appears to constitute crucial steps in the transition of a normal to a neoplastic cell. Several factors have been identified that control positively or negatively the proliferation and differentiation of tracheobronchial epithelial cells. These factors include EGF/TGF alpha, TGF beta, insulin/IGFI, KGF, certain cytokines, retinoids, and activators of protein kinase C. Studies with neoplastic cells have identified several protooncogenes and tumor suppressor genes whose gene products are involved in the regulation of cell growth of normal tracheobronchial epithelial cells, and when mutated, lost, or activated, bring about a neoplastic phenotype. Future studies on the precise function of these genes will help to elucidate the mechanisms by which proliferation and differentiation in normal tracheobronchial epithelial cells are regulated and help to understand the molecular changes involved in diseases such as cancer.

Expression of nuclear retinoic acid receptors in wild-type and mutant embryonal carcinoma PCC4.aza1R cells

Retinoic acid (RA) induces differentiation of murine embryonal carcinoma PCC4.aza1R cells. In this study, the expression of nuclear retinoic acid receptors (RARs) in PCC4.aza1R cells is examined. Analyses of [3H]RA-labeled nuclear extracts prepared from PCC4.aza1R cells by size-exclusion high-performance liquid chromatography demonstrated the presence of a specific RA-binding activity that migrated with a molecular weight of approximately 50,000. More than 95% of this binding activity was associated with the nuclear fraction. In contrast to cytosolic retinoic acid-binding protein, the RARs bound RA analogues of the Ch-series very effectively. Northern blot analyses of total RNA with complementary DNA probes specific for RAR alpha, RAR beta, and RAR gamma showed that PCC4.aza1R cells contain predominantly transcripts encoding RAR alpha and RAR gamma; RAR beta transcripts were undetectable. Treatment of PCC4.aza1R cells with RA increased the levels of RAR beta mRNA in a dose- and time-dependent manner. The RA concentration for half-maximum induction of RAR beta mRNA was 1 nM. An increase in RAR beta mRNA was detectable as early as 2 h after the addition of RA. This increase was not abrogated by cycloheximide, suggesting that protein synthesis is not required for this response. The ability of several retinoids to increase RAR beta mRNA levels in PCC4.aza1R cells correlated well with their binding affinity to the RARs but not with their binding affinity to cytosolic retinoic acid-binding protein. Two mutant cell lines, PCC4(RA)-1 and (RA)-2, which do not undergo differentiation after RA treatment, contained levels of RAR-binding activity very similar to those of the parental cells.(ABSTRACT TRUNCATED AT 250 WORDS)

Regulation of transglutaminase type II by transforming growth factor-beta 1 in normal and transformed human epidermal keratinocytes

This study examines the effect of transforming growth factor-beta 1 (TGF-beta 1) on the expression of Type I and II transglutaminase in normal human epidermal keratinocytes (NHEK cells). Treatment of undifferentiated NHEK cells with 100 pM TGF-beta 1 caused a 10- to 15-fold increase in the activity of a soluble transglutaminase. Based on its cellular distribution and immunoreactivity this transglutaminase was identified as Type II (tissue) transglutaminase. TGF-beta 1 did not enhance the levels of the membrane-bound Type I (epidermal) transglutaminase activity which is induced during squamous cell differentiation and did not increase Type II transglutaminase activity in differentiated NHEK cells. Several SV40 large T antigen-immortalized NHEK cell lines also exhibited a dramatic increase in transglutaminase Type II activity after TGF-beta 1 treatment; however, TGF-beta 1 did not induce any significant change in transglutaminase activity in the carcinoma-derived cell lines SCC-13, SCC-15, and SQCC/Y1. Half-maximal stimulation of transglutaminase Type II activity in NHEK cells occurred at a dose of 15 pM TGF-beta 1. TGF-beta 2 was about equally effective. This enhancement in transglutaminase activity was related to an increase in the amount of transglutaminase Type II protein as indicated by immunoblot analysis. Northern blot analyses using a specific cDNA probe for Type II transglutaminase showed that exposure of NHEK cells to TGF-beta 1 caused a marked increase in the mRNA levels of this enzyme which could be observed as early as 4 h after the addition of TGF-beta 1. Maximal induction of transglutaminase Type II mRNA occurred between 18 and 24 h. The increase in Type II transglutaminase mRNA levels was blocked by the presence of cycloheximide, suggesting that this increase in mRNA by TGF-beta 1 is dependent on protein synthesis.

Identification and characterization of nuclear retinoic acid-binding activity in human myeloblastic leukemia HL-60 cells

Specific [3H]retinoic acid (RA)-binding sites in nuclear and cytosolic extracts prepared from human myeloblastic leukemia HL-60 cells have been detected by sucrose density gradient sedimentation and size-exclusion high-performance liquid chromatography (HPLC) analyses. This RA-binding activity migrated as a single peak with an apparent molecular weight of 50,000 and greater than 95% of the total binding activity was associated with the nuclear extract. Nuclear extracts prepared from COS-1 cells transfected with an expression vector for the nuclear RA receptors RAR alpha or RAR beta were enriched (20- to 100-fold) with a RA-binding activity that coeluted by size-exclusion HPLC with the putative RAR from HL-60 cells. The HL-60 nuclear receptor exhibited high-affinity binding of RA and its benzoic acid analogs Ch55, Ch30, Ro 13-7410, and SRI 6409-40 and low-affinity binding of retinol, Ro 8-8717, and SRI 5442-60, correlating well with the biological activity of these compounds in HL-60 cells. Saturation binding and Scatchard plot analyses of the binding of RA to the nuclear HL-60 receptor yielded an apparent dissociation constant of approximately 0.46 nM and 1400 +/- 100 receptor sites per cell. Northern blot analyses of poly(A)+ RNA with cDNA probes specific for RAR alpha and RAR beta indicated that HL-60 cells contain predominantly transcripts encoded by the RAR alpha gene. Our results suggest that the observed nuclear RA-binding activity in HL-60 cells might mediate the action of RA in these cells.