Health-related quality of life in survivors of advanced melanoma treated with anti-PD1-based immune checkpoint inhibitors

BACKGROUND

Immune checkpoint inhibitors (ICIs) have significantly improved survival in advanced melanoma but are associated with immune-related adverse events (irAEs). This single center, cross-sectional survey aimed to describe the long-term symptom burden and impact on health-related quality of life (HRQL) of advanced melanoma patients with sustained disease control following treatment with ICIs.

METHODS

Advanced melanoma patients (stage IIB, III or IV, AJCCv8), treated with anti-PD1-based ICIs, who were off-treatment and had at least 6 months follow-up from their last infusion with an ongoing response in the metastatic setting or no evidence of disease recurrence in the adjuvant setting. A paper-based questionnaire, consisting of the EORTC QLQ-C30, EORTC QLQ-FA12, and the PRO-CTCAE was administered.

RESULTS

Of 90 participants, 61 (68%) completed the questionnaire; 40 received single-agent anti-PD1, and 21 anti-PD1/anti-CTLA4. Thirty-three (54%) were treated in the adjuvant setting. At the time of enrolment, 31 (51%) participants had active treatment for a previous irAE. Overall, 18/61 (30%) participants reported long-term symptoms and trouble in physical and emotional functioning. Physical fatigue was common and interfered with daily activities (n = 12, 20%). In the PRO-CTCAE questionnaire, muscle ache (n = 12, 20%) and joint ache (n = 9, 15%) were commonly reported. Despite this, participants reported overall good health (6.00, range 2.00-7.00) and reasonable level of HRQL (6.00, range 3.00-7.00).

DISCUSSION

Melanoma survivors experience long-term symptoms in physical and psychosocial HRQL domains after ICI treatment. These results underline the importance to address existing gaps in survivorship care, implement these findings in clinical practice and increase awareness for long-term symptoms in these patients.

Identifying the potential origin of mucin in primary cutaneous mucinoses-A retrospective study and analysis using histopathology and multiplex fluorescence staining

BACKGROUND

Primary cutaneous mucinoses (PCM) are rare diseases characterized by dermal or follicular mucin deposits.

OBJECTIVES

A retrospective study characterizing PCM to compare dermal with follicular mucin to identify its potential origin on a single-cell level.

MATERIAL AND METHODS

Patients diagnosed with PCM between 2010 and 2020 at our department were included in this study. Biopsy specimens were stained using conventional mucin stains (Alcian blue, PAS) and MUC1 immunohistochemical staining. Multiplex fluorescence staining (MFS) was used to investigate which cells were associated with MUC1 expression in select cases.

RESULTS

Thirty-one patients with PCM were included, 14 with follicular mucinosis (FM), 8 with reticular erythematous mucinosis, 2 with scleredema, 6 with pretibial myxedema and one patient with lichen myxedematosus. In all 31 specimens, mucin stained positive for Alcian blue and negative for PAS. In FM, mucin deposition was exclusively found in hair follicles and sebaceous glands. None of the other entities showed mucin deposits in follicular epithelial structures. Using MFS, all cases showed CD4+ and CD8+ T cells, tissue histiocytes, fibroblasts and pan-cytokeratin+ cells. These cells expressed MUC1 at different intensities. MUC1 expression in tissue histiocytes, fibroblasts, CD4+ and CD8+ T cells, and follicular epithelial cells of FM was significantly higher than the same cell types in the dermal mucinoses (p < 0.001). CD8+ T cells were significantly more involved in expression of MUC1 than all other analysed cell types in FM. This finding was also significant in comparison with dermal mucinoses.

CONCLUSION

Various cell types seem to contribute to mucin production in PCM. Using MFS, we showed that CD8+ T cells seem to be more involved in the production of mucin in FM than in dermal mucinoses, which could indicate that mucin in dermal and follicular epithelial mucinoses have different origins.

The glucose-sensing transcription factor MLX balances metabolism and stress to suppress apoptosis and maintain spermatogenesis

Male germ cell (GC) production is a metabolically driven and apoptosis-prone process. Here, we show that the glucose-sensing transcription factor (TF) MAX-Like protein X (MLX) and its binding partner MondoA are both required for male fertility in the mouse, as well as survival of human tumor cells derived from the male germ line. Loss of Mlx results in altered metabolism as well as activation of multiple stress pathways and GC apoptosis in the testes. This is concomitant with dysregulation of the expression of male-specific GC transcripts and proteins. Our genomic and functional analyses identify loci directly bound by MLX involved in these processes, including metabolic targets, obligate components of male-specific GC development, and apoptotic effectors. These in vivo and in vitro studies implicate MLX and other members of the proximal MYC network, such as MNT, in regulation of metabolism and differentiation, as well as in suppression of intrinsic and extrinsic death signaling pathways in both spermatogenesis and male germ cell tumors (MGCTs).

Loss of MGA repression mediated by an atypical polycomb complex promotes tumor progression and invasiveness

MGA, a transcription factor and member of the MYC network, is mutated or deleted in a broad spectrum of malignancies. As a critical test of a tumor suppressive role, we inactivated Mga in two mouse models of non-small cell lung cancer using a CRISPR-based approach. MGA loss significantly accelerated tumor growth in both models and led to de-repression of non-canonical Polycomb ncPRC1.6 targets, including genes involved in metastasis and meiosis. Moreover, MGA deletion in human lung adenocarcinoma lines augmented invasive capabilities. We further show that MGA-MAX, E2F6, and L3MBTL2 co-occupy thousands of promoters and that MGA stabilizes these ncPRC1.6 subunits. Lastly, we report that MGA loss also induces a pro-growth effect in human colon organoids. Our studies establish MGA as a bona fide tumor suppressor in vivo and suggest a tumor suppressive mechanism in adenocarcinomas resulting from widespread transcriptional attenuation of MYC and E2F target genes mediated by MGA-MAX associated with a non-canonical Polycomb complex.

Myc/Mycn-mediated glycolysis enhances mouse spermatogonial stem cell self-renewal

Here, Kanatsu-Shinohara et al. investigated the mechanisms underlying Myc regulation of spermatogonial stem cell (SSC) fate. Their findings suggest that Myc-mediated glycolysis is an important factor that increases the frequency of SSC self-renewal division.

Myc plays critical roles in the self-renewal division of various stem cell types. In spermatogonial stem cells (SSCs), Myc controls SSC fate decisions because Myc overexpression induces enhanced self-renewal division, while depletion of Max, a Myc-binding partner, leads to meiotic induction. However, the mechanism by which Myc acts on SSC fate is unclear. Here we demonstrate a critical link between Myc/Mycn gene activity and glycolysis in SSC self-renewal. In SSCs, Myc/Mycn are regulated by Foxo1, whose deficiency impairs SSC self-renewal. Myc/Mycn-deficient SSCs not only undergo limited self-renewal division but also display diminished glycolytic activity. While inhibition of glycolysis decreased SSC activity, chemical stimulation of glycolysis or transfection of active Akt1 or Pdpk1 (phosphoinositide-dependent protein kinase 1 ) augmented self-renewal division, and long-term SSC cultures were derived from a nonpermissive strain that showed limited self-renewal division. These results suggested that Myc-mediated glycolysis is an important factor that increases the frequency of SSC self-renewal division.

Genetic requirement for Mycl and efficacy of RNA Pol I inhibition in mouse models of small cell lung cancer

Kim et al. isolated preneoplastic neuroendocrine cells from a mouse model of small cell lung cancer (SCLC) and found that ectopic expression of L-Myc conferred tumor-forming capacity. An RNA polymerase I inhibitor used to target rRNA synthesis resulted in significant tumor inhibition in an autochthonous Rb/p53-deleted mouse SCLC model.

Small cell lung cancer (SCLC) is a devastating neuroendocrine carcinoma. MYCL (L-Myc) is frequently amplified in human SCLC, but its roles in SCLC progression are poorly understood. We isolated preneoplastic neuroendocrine cells from a mouse model of SCLC and found that ectopic expression of L-Myc, c-Myc, or N-Myc conferred tumor-forming capacity. We focused on L-Myc, which promoted pre-rRNA synthesis and transcriptional programs associated with ribosomal biogenesis. Deletion of Mycl in two genetically engineered models of SCLC resulted in strong suppression of SCLC. The high degree of suppression suggested that L-Myc may constitute a therapeutic target for a broad subset of SCLC. We then used an RNA polymerase I inhibitor to target rRNA synthesis in an autochthonous Rb/p53-deleted mouse SCLC model and found significant tumor inhibition. These data reveal that activation of RNA polymerase I by L-Myc and other MYC family proteins provides an axis of vulnerability for this recalcitrant cancer.

An exploratory study investigating the metabolic activity and local cytokine profile in patients with melanoma treated with pazopanib and paclitaxel

BACKGROUND

There is a medical need for new drugs in patients with BRAF wild-type metastatic melanoma. Pazopanib is a multitarget tyrosine kinase inhibitor with antitumour and antiangiogenic activity.

OBJECTIVES

The primary aim was to investigate the metabolic response to pazopanib monotherapy and pazopanib plus paclitaxel in patients with BRAF wild-type melanoma. Secondary end points were the early cytokine and chemokine profiles and histological findings.

METHODS

Pazopanib (400 mg twice daily) was administered orally from days 1 to 10 and from days 14 to 70. An intravenous infusion with paclitaxel (150 mg m^-2 body surface) was administered on days 14, 35 and 56. Metabolic response evaluation was performed before treatment, after treatment with pazopanib (day 10) and after treatment with pazopanib and paclitaxel (day 70). Skin biopsy of metastatic tissue for chemokine and cytokine expression analysis and histology and immunohistochemistry (CD68, CD163) evaluation, and blood samples were taken at the same time points.

RESULTS

Two patients failed screening and 17 were dosed. Of 67 adverse events, nine (13%) were grade 3 or 4. Five of 14 evaluable patients had a partial metabolic response at day 10 under pazopanib monotherapy. The response rate at day 70 under combined pazopanib-paclitaxel treatment was 0%. Immunohistochemistry revealed an increase of M2-like macrophages in nonresponders compared with responders. We observed a significant upregulation of five cytokines (CXCL1, CXCL2, CXCL13, CCL22 and SPP1) in responding vs. nonresponding lesions. Overall, the median progression-free survival was 70 days (range 5-331), which did not differ significantly between responders (148 days) and nonresponders (70 days, P = 0·17).

CONCLUSIONS

In this patient population pazopanib efficacy was limited. Response is associated with low M2-like macrophage density and increased expression of several chemokines.

Investigation of Ramsey spectroscopy in a lin-par-lin Ramsey coherent population trapping clock with dispersion detection

We demonstrate that the lin-par-lin Ramsey coherent population trapping ⁸⁷Rb clock using a dispersion detection technique has a promising performance. We theoretically and experimentally investigate the signal-to-noise ratio of the Ramsey spectrum signal by varying the relative angle of the polarizer and analyzer as well as the magnetic field. Based on the experimental results, the optimized relative angle and magnetic field are determined. This kind of atomic clock is attractive for the development of compact, high performance vapor clock based on CPT.

Deregulated Myc requires MondoA/Mlx for metabolic reprogramming and tumorigenesis

Deregulated Myc transcriptionally reprograms cell metabolism to promote neoplasia. Here we show that oncogenic Myc requires the Myc superfamily member MondoA, a nutrient-sensing transcription factor, for tumorigenesis. Knockdown of MondoA, or its dimerization partner Mlx, blocks Myc-induced reprogramming of multiple metabolic pathways, resulting in apoptosis. Identification and knockdown of genes coregulated by Myc and MondoA have allowed us to define metabolic functions required by deregulated Myc and demonstrate a critical role for lipid biosynthesis in survival of Myc-driven cancer. Furthermore, overexpression of a subset of Myc and MondoA coregulated genes correlates with poor outcome of patients with diverse cancers. Coregulation of cancer metabolism by Myc and MondoA provides the potential for therapeutics aimed at inhibiting MondoA and its target genes.

Abstract B30: Synthetic lethal interactions between members of the extended MYC network during metabolic reprograming in MYC-driven cancers

In many tumors, the increased biosynthesis and growth required for tumor progression is achieved by metabolic reprogramming associated with the activation of specific oncogenes. This can manifest itself as a shift to aerobic glycolysis coupled with increased anabolic metabolism or altered catabolism. This is especially relevant to tumors with activated Myc, in which Myc-Max heterodimers are transcriptional mediators of biosynthesis and growth. Work from many labs has implicated Myc in multiple aspects of the shift to increased glucose and glutamine uptake and stimulation of mitochondrial biogenesis and activity. Importantly, Myc-Max does not function alone, but within the context of an extended transcriptional network comprised of the Max-binding, Myc-antagonizing Mxd proteins as well as the Max-like protein, Mlx, and its heterodimerization partners MondoA and ChREBP (also known as MondoB)

In order to understand how functional interactions and dependencies within the network influence Myc's role in normal and neoplastic cell behavior, we examined cell growth after siRNA mediated knockdown (KD) of different Max and Mlx network members in a panel of c-Myc and N-myc inducible cell lines. Results showed a synthetic lethal interaction between high level of Myc expression and loss of MondoA, or its heterodimeric binding partner Mlx. This synthetic effect was observed both in tissue culture and in mouse xenografts.

By employing transcriptomic and metabolomic analyses we show that the MondoA-Mlx arm of the extended Max-Mlx network is required for deregulated Myc to drive metabolic reprograming and maintain survival and growth of these tumor cell. We further show that a subset of Myc-induced genes involved in metabolism require MondoA for full expression. Interestingly, knockdown of a number of these genes alone, which control a variety of metabolic pathways, can recapitulate the synthetic lethal interaction with deregulated Myc. Taken together, these data suggest that both Myc-Max and MondoA-Mlx complexes coordinately regulate the transcriptional activity of a group of genes critical for Myc's ability to reprogram tumor metabolism. The integration of Myc and MondoA functions may serve to link Myc to nutrient sensing and to augment metabolic flexibility within the evolving tumor.

PC and DD contributed equally to this work.

This research supported by NIH/NCI grant R37CA57138.

Citation Format: Patrick A. Carroll, Daniel Diolaiti, Lisa McFerrin, Michelle Hulrich, Pei Feng Cheng, Haiwei Gu, Danijel Djukovic, Daniel Raftery, Robert N. Eisenman. Synthetic lethal interactions between members of the extended MYC network during metabolic reprograming in MYC-driven cancers. [abstract]. In: Proceedings of the AACR Precision Medicine Series: Synthetic Lethal Approaches to Cancer Vulnerabilities; May 17-20, 2013; Bellevue, WA. Philadelphia (PA): AACR; Mol Cancer Ther 2013;12(5 Suppl):Abstract nr B30.

Myc influences global chromatin structure

The family of myc proto-oncogenes encodes transcription factors (c-, N-, and L-Myc) that regulate cell growth and proliferation and are involved in the etiology of diverse cancers. Myc proteins are thought to function by binding and regulating specific target genes. Here we report that Myc proteins are required for the widespread maintenance of active chromatin. Disruption of N-myc in neuronal progenitors and other cell types leads to nuclear condensation accompanied by large-scale changes in histone modifications associated with chromatin inactivation, including hypoacetylation and altered methylation. These effects are largely reversed by exogenous Myc as well as by differentiation and are mimicked by the Myc antagonist Mad1. The first chromatin changes are evident within 6 h of Myc loss and lead to changes in chromatin structure. Myc widely influences chromatin in part through upregulation of the histone acetyltransferase GCN5. This study provides the first evidence for regulation of global chromatin structure by an oncoprotein and may explain the broad effects of Myc on cell behavior and tumorigenesis.

The mSin3A chromatin-modifying complex is essential for embryogenesis and T-cell development

The corepressor mSin3A is the core component of a chromatin-modifying complex that is recruited by multiple gene-specific transcriptional repressors. In order to understand the role of mSin3A during development, we generated constitutive germ line as well as conditional msin3A deletions. msin3A deletion in the developing mouse embryo results in lethality at the postimplantation stage, demonstrating that it is an essential gene. Blastocysts derived from preimplantation msin3A null embryos and mouse embryo fibroblasts (MEFs) lacking msin3A display a significant reduction in cell division. msin3A null MEFs also show mislocalization of the heterochromatin protein, HP1alpha, without alterations in global histone acetylation. Heterozygous msin3A(+/-) mice with a systemic twofold decrease in mSin3A protein develop splenomegaly as well as kidney disease indicative of a disruption of lymphocyte homeostasis. Conditional deletion of msin3A from developing T cells results in reduced thymic cellularity and a fivefold decrease in the number of cytotoxic (CD8) T cells, while helper (CD4) T cells are unaffected. We show that CD8 development is dependent on mSin3A at a step downstream of T-cell receptor signaling and that loss of mSin3A specifically decreases survival of double-positive and CD8 T cells. Thus, msin3A is a pleiotropic gene which, in addition to its role in cell cycle progression, is required for the development and homeostasis of cells in the lymphoid lineage.

N-myc is essential during neurogenesis for the rapid expansion of progenitor cell populations and the inhibition of neuronal differentiation

To address the role of N-myc in neurogenesis and in nervous system tumors, it was conditionally disrupted in neuronal progenitor cells (NPCs) with a nestin-Cre transgene. Null mice display ataxia, behavioral abnormalities, and tremors that correlate with a twofold decrease in brain mass that disproportionately affects the cerebellum (sixfold reduced in mass) and the cerebral cortex, both of which show signs of disorganization. In control mice at E12.5, we observe a domain of high N-Myc protein expression in the rapidly proliferating cerebellar primordium. Targeted deletion of N-myc results in severely compromised proliferation as shown by a striking decrease in S phase and mitotic cells as well as in cells expressing the Myc target gene cyclin D2, whereas apoptosis is unaffected. Null progenitor cells also have comparatively high levels of the cdk inhibitors p27(Kip1) and p18(Ink4c), whereas p15(Ink4b), p21(Cip1), and p19(Ink4d) levels are unaffected. Many null progenitors also exhibit altered nuclear morphology and size. In addition, loss of N-myc disrupts neuronal differentiation as evidenced by ectopic staining of the neuron specific marker betaTUBIII in the cerebrum. Furthermore, in progenitor cell cultures derived from null embryonic brain, we observe a dramatic increase in neuronal differentiation compared with controls. Thus, N-myc is essential for normal neurogenesis, regulating NPC proliferation, differentiation, and nuclear size. Its effects on proliferation and differentiation appear due, at least in part, to down-regulation of a specific subset of cyclin-dependent kinase inhibitors.

MyoD-positive myoblasts are present in mature fetal organs lacking skeletal muscle

The epiblast of the chick embryo gives rise to the ectoderm, mesoderm, and endoderm during gastrulation. Previous studies revealed that MyoD-positive cells were present throughout the epiblast, suggesting that skeletal muscle precursors would become incorporated into all three germ layers. The focus of the present study was to examine a variety of organs from the chicken fetus for the presence of myogenic cells. RT-PCR and in situ hybridizations demonstrated that MyoD-positive cells were present in the brain, lung, intestine, kidney, spleen, heart, and liver. When these organs were dissociated and placed in culture, a subpopulation of cells differentiated into skeletal muscle. The G8 antibody was used to label those cells that expressed MyoD in vivo and to follow their fate in vitro. Most, if not all, of the muscle that formed in culture arose from cells that expressed MyoD and G8 in vivo. Practically all of the G8-positive cells from the intestine differentiated after purification by FACS. This population of ectopically located cells appears to be distinct from multipotential stem cells and myofibroblasts. They closely resemble quiescent, stably programmed skeletal myoblasts with the capacity to differentiate when placed in a permissive environment.

Myc and Max homologs in Drosophila

The proteins encoded by the myc proto-oncogene family are involved in cell proliferation, apoptosis, differentiation, and neoplasia. Myc acts through dimerization with Max to bind DNA and activate transcription. Homologs of the myc and max genes were cloned from the fruit fly Drosophila melanogaster and their protein products (dMyc and dMax) were shown to heterodimerize, recognize the same DNA sequence as their vertebrate homologs, and activate transcription. The dMyc protein is likely encoded by the Drosophila gene diminutive (dm), a mutation in which results in small body size and female sterility caused by degeneration of the ovaries. These findings indicate a potential role for Myc in germ cell development and set the stage for genetic analysis of Myc and Max.

Identification of a new family of tissue-specific basic helix-loop-helix proteins with a two-hybrid system

With modified two-hybrid technology, we have isolated a member of a new family of basic helix-loop-helix (bHLH) transcription factors. Thing1 (Th1) was identified in a screen of a mouse embryo cDNA library as a partner for the Drosophila E protein daughterless. RNA in situ hybridization and reverse transcriptase-PCR demonstrate a stage- and tissue-specific distribution for the expression of Th1. Although tissue specific, the expression pattern of Th1 is fairly complex. During development, Th1 mRNA is widely expressed in extraembryonic tissues, portions of the heart, autonomic ganglia, the gut, and pharyngeal arches. At embryonic day 7.5 (E7.5), extraembryonic derivatives show robust Th1 expression. By E8.5, expression in the embryonic heart becomes detectable. During the next 2 days of development, the signal also includes gut and pharyngeal arches. Predominant expression at E13.5 is in neural crest derivatives, especially the autonomic nervous system and adrenal medulla. Expression of Th1 persists in the adult, in which it is localized to the smooth muscle cells of the gut. In vitro, Th1 protein recognizes a set of DNA sites that are more degenerate than has been determined for other bHLH factors, indicating a reduced binding specificity. Transient transfection of NIH 3T3 cells with GAL4-Th1 fusions reveals a repression activity mediated by the Th1 bHLH domain. In combination, these properties define Th1 as a new bHLH protein with a unique set of properties.

Use of a conditional MyoD transcription factor in studies of MyoD trans-activation and muscle determination

DNA sequences encoding the hormone-binding domains of several steroid hormone receptors were fused in frame to the MyoD gene. When the gene for this chimeric protein was expressed in NIH 3T3 or 10T1/2 fibroblasts, these cells displayed hormone-dependent induction of myogenesis. Our experiments focused on cell lines expressing estrogen receptor-MyoD chimeras. Induction of these lines in the presence of estradiol and an inhibitor of protein synthesis, cycloheximide, resulted in the activation of the endogenous myogenin gene but did not activate the muscle-specific creatine kinase or cardiac alpha-actin gene. This result suggests that MyoD is not a "direct" activator of these downstream myogenic genes but must first activate myogenin as an intermediary. Once muscle is induced by estrogen receptor-MyoD the muscle phenotype is very stable and does not need the continued presence of estradiol for its maintenance.

Retinoic acid perturbs the expression of Xhox.lab genes and alters mesodermal determination in Xenopus laevis

Retinoic acid (RA) treatment of Xenopus laevis embryos leads to anterior truncation of the body axis (Durston et al. 1989; Sive et al. 1990). These initial studies suggested that RA may play a role in the patterning of the primary body axis. At least one target of RA was shown previously to be dorsal ectoderm. In this report we extend this observation and also ask whether RA alters the determination and inducing capacity of mesodermal tissue. To facilitate this analysis we isolated the homeo-domain-containing genes Xhox.lab1 and Xhox.lab2. These genes were expressed in both ectoderm and mesoderm during the RA-sensitive period and were strongly induced by RA in both germ layers. In particular, anterior regions expressed low levels of Xhox.lab RNAs in untreated embryos but showed increased expression after RA application. We show further that although RA-treated embryos contained anterior-inducing mesoderm, the amount of this activity appeared to be lower than that of controls. Additionally, we document that RA suppressed lateral (muscle) and ventral (blood) mesoderm differentiation. The data indicate that RA alters mesodermal determination and causes axial perturbation both by depressing the ability of dorsal mesoderm to induce anterior structures and by altering the response of dorsal ectoderm to induction. These analyses suggest that Xhox.lab genes may be responsible, in part, for mediating the RA effect.

The MyoD DNA binding domain contains a recognition code for muscle-specific gene activation

A 60 amino acid domain of the myogenic determination gene MyoD is necessary and sufficient for sequence-specific DNA binding in vitro and myogenic conversion of transfected C3H10T1/2 cells. We show that a highly basic region, immediately upstream of the helix-loop-helix (HLH) oligomerization motif, is required for MyoD DNA binding in vitro. Replacing helix1, helix2, or the loop of MyoD with the analogous sequence of the Drosophila T4 achaete-scute protein (required for peripheral neurogenesis) has no substantial effect on DNA binding in vitro or muscle-specific gene activation in transfected C3H10T1/2 cells. However, replacing the basic region of MyoD with the analogous sequence of other HLH proteins (the immunoglobulin enhancer binding E12 protein or T4 achaete scute protein) allows DNA binding in vitro, yet abolishes muscle-specific gene activation. These findings suggest that a recognition code that determines muscle-specific gene activation lies within the MyoD basic region and that the capacity for specific DNA binding is insufficient to activate the muscle program.

MyoD1: a nuclear phosphoprotein requiring a Myc homology region to convert fibroblasts to myoblasts

Expression of a complementary DNA (cDNA) encoding the mouse MyoD1 protein in a variety of fibroblast and adipoblast cell lines converts them to myogenic cells. Polyclonal antisera to fusion proteins containing the MyoD1 sequence show that MyoD1 is a phosphoprotein present in the nuclei of proliferating myoblasts and differentiated myotubes but not expressed in 10T1/2 fibroblasts or other nonmuscle cell types. Functional domains of the MyoD1 protein were analyzed by site-directed deletional mutagenesis of the MyoD1 cDNA. Deletion of a highly basic region (residues 102 to 135) interferes with both nuclear localization and induction of myogenesis. Deletion of a short region (residues 143 to 162) that is similar to a conserved region in the c-Myc family of proteins eliminates the ability of the MyoD1 protein to initiate myogenesis but does not alter nuclear localization. Deletions of regions spanning the remainder of MyoD1 did not affect nuclear localization and did not inhibit myogenesis. Furthermore, expression of only 68 amino acids of MyoD1, containing the basic and the Myc similarity domains, is sufficient to activate myogenesis in stably transfected 10T1/2 cells. Genetic analysis maps the MyoD1 gene to mouse chromosome 7 and human chromosome 11.

Expression of transfected DNA depends on DNA topology

Supercoiled DNAs, especially those containing enhancers, yield markedly higher levels of expression than linearized DNA when transfected into CV-1 cells or L cells. Different templates, linear or supercoiled, enhancer-containing or not, saturate for expression at 2 micrograms DNA per dish, suggesting that one role for enhancers and supercoiling is to increase the efficiency with which the same limiting component is used. Plasmids containing only enhancers or only promoters do not compete for expression with an enhancer-driven gene. However, plasmids that contain both enhancers and promoters do complete, suggesting that a second role for enhancers is to increase the binding of a limiting transcription factor. Linear and supercoiled enhancer-promoter plasmids compete equivalently. This suggests that supercoiling affects the ability of transcription factors to activate a given promoter, once bound.

Tissue-specific and species-specific monoclonal antibodies to avian red cell nuclear proteins

In order to identify potential red cell-specific regulatory proteins and to define additional red cell-specific markers, we have isolated a series of hybridomas that produce monoclonal antibodies that react with nuclear preparations from avian red blood cells. Several antibodies have been well characterized for their tissue- and species-specific reactions by using solid-phase and protein-transfer radioimmunoassays as well as immunofluorescence. These antibodies should allow isolation and characterization of individual nuclear proteins that are tissue and species specific and may prove useful for the study of gene expression in the erythropoietic system. The majority of the well-characterized antibodies appear to have tissue-specific properties. However, three antibodies react with all tested chicken tissues; one of these reacts with multiple peptides in a pattern that varies qualitatively and quantitatively between the tissues. This may reflect a common protein domain or modification that is used in several different tissues for similar functions but is nevertheless present in an overall protein framework that is tissue specific. Because the major fraction of the hybridomas initially produced is tissue specific, we presume that the immune system selects for tissue-specific determinants. This property of the immune system may prove to be a useful general feature of this type of analysis.