From modulation of cellular plasticity to potentiation of therapeutic resistance: new and emerging roles of MYB transcription factors in human malignancies

MYB transcription factors are encoded by a large family of highly conserved genes from plants to vertebrates. There are three members of the MYB gene family in human, namely, MYB, MYBL1, and MYBL2 that encode MYB/c-MYB, MYBL1/A-MYB, and MYBL2/B-MYB, respectively. MYB was the first member to be identified as a cellular homolog of the v-myb oncogene carried by the avian myeloblastosis virus (AMV) causing leukemia in chickens. Under the normal scenario, MYB is predominantly expressed in hematopoietic tissues, colonic crypts, and neural stem cells and plays a role in maintaining the undifferentiated state of the cells. Over the years, aberrant expression of MYB genes has been reported in several malignancies and recent years have witnessed tremendous progress in understanding of their roles in processes associated with cancer development. Here, we review various MYB alterations reported in cancer along with the roles of MYB family proteins in tumor cell plasticity, therapy resistance, and other hallmarks of cancer. We also discuss studies that provide mechanistic insights into the oncogenic functions of MYB transcription factors to identify potential therapeutic vulnerabilities.

Mitochondrial Translocase TOMM22 Is Overexpressed in Pancreatic Cancer and Promotes Aggressive Growth by Modulating Mitochondrial Protein Import and Function

Pancreatic cancer has the worst prognosis among all cancers, underscoring the need for improved management strategies. Dysregulated mitochondrial function is a common feature in several malignancies, including pancreatic cancer. Although mitochondria have their own genome, most mitochondrial proteins are nuclear-encoded and imported by a multi-subunit translocase of the outer mitochondrial membrane (TOMM). TOMM22 is the central receptor of the TOMM complex and plays a role in complex assembly. Pathobiologic roles of TOMM subunits remain largely unexplored. Here we report that TOMM22 protein/mRNA is overexpressed in pancreatic cancer and inversely correlated with disease outcomes. TOMM22 silencing decreased, while its forced overexpression promoted the growth and malignant potential of the pancreatic cancer cells. Increased import of several mitochondrial proteins, including those associated with mitochondrial respiration, was observed upon TOMM22 overexpression which was associated with increased RCI activity, NAD+/NADH ratio, oxygen consumption rate, membrane potential, and ATP production. Inhibition of RCI activity decreased ATP levels and suppressed pancreatic cancer cell growth and malignant behavior confirming that increased TOMM22 expression mediated the phenotypic changes via its modulation of mitochondrial protein import and functions. Altogether, these results suggest that TOMM22 overexpression plays a significant role in pancreatic cancer pathobiology by altering mitochondrial protein import and functions.

IMPLICATIONS

TOMM22 bears potential for early diagnostic/prognostic biomarker development and therapeutic targeting for better management of patients with pancreatic cancer.

Profiling mitochondrial DNA mutations in tumors and circulating extracellular vesicles of triple-negative breast cancer patients for potential biomarker development

Early detection and recurrence prediction are challenging in triple-negative breast cancer (TNBC) patients. We aimed to develop mitochondrial DNA (mtDNA)-based liquid biomarkers to improve TNBC management. Mitochondrial genome (MG) enrichment and next-generation sequencing mapped the entire MG in 73 samples (64 tissues and 9 extracellular vesicles [EV] samples) from 32 metastatic TNBCs. We measured mtDNA and cardiolipin (CL) contents, NDUFB8, and SDHB protein expression in tumors and in corresponding circulating EVs. We identified 168 nonsynonymous mtDNA mutations, with 73% (123/186) coding and 27% (45/168) noncoding in nature. Twenty percent of mutations were nucleotide transversions. Respiratory complex I (RCI) was the key target, which harbored 44% (74/168) of the overall mtDNA mutations. A panel of 11 hotspot mtDNA mutations was identified among 19%-38% TNBCs, which were detectable in the serum-derived EVs with 82% specificity. Overall, 38% of the metastatic tumor-signature mtDNA mutations were traceable in the EVs. An appreciable number of mtDNA mutations were homoplasmic (18%, 31/168), novel (14%, 23/168), and potentially pathogenic (9%, 15/168). The overall and RCI-specific mtDNA mutational load was higher in women with African compared to European ancestry accompanied by an exclusive abundance of respiratory complex (RC) protein NDUFB8 (RCI) and SDHB (RCII) therein. Increased mtDNA (p < 0.0001) content was recorded in both tumors and EVs along with an abundance of CL (p = 0.0001) content in the EVs. Aggressive tumor-signature mtDNA mutation detection and measurement of mtDNA and CL contents in the EVs bear the potential to formulate noninvasive early detection and recurrence prediction strategies.

MYB sustains hypoxic survival of pancreatic cancer cells by facilitating metabolic reprogramming

Extensive desmoplasia and poor vasculature renders pancreatic tumors severely hypoxic, contributing to their aggressiveness and therapy resistance. Here, we identify the HuR/MYB/HIF1α axis as a critical regulator of the metabolic plasticity and hypoxic survival of pancreatic cancer cells. HuR undergoes nuclear-to-cytoplasmic translocation under hypoxia and stabilizes MYB transcripts, while MYB transcriptionally upregulates HIF1α. Upon MYB silencing, pancreatic cancer cells fail to survive and adapt metabolically under hypoxia, despite forced overexpression of HIF1α. MYB induces the transcription of several HIF1α-regulated glycolytic genes by directly binding to their promoters, thus enhancing the recruitment of HIF1α to hypoxia-responsive elements through its interaction with p300-dependent histone acetylation. MYB-depleted pancreatic cancer cells exhibit a dramatic reduction in tumorigenic ability, glucose-uptake and metabolism in orthotopic mouse model, even after HIF1α restoration. Together, our findings reveal an essential role of MYB in metabolic reprogramming that supports pancreatic cancer cell survival under hypoxia.

Detection of mitochondrial DNA mutations in circulating mitochondria-originated extracellular vesicles for potential diagnostic applications in pancreatic adenocarcinoma

There is a complete lack of highly sensitive and specific biomarkers for early pancreatic ductal adenocarcinoma (PDAC) diagnosis, limiting multi-modal therapeutic options. Mitochondrial DNA (mtDNA) is an excellent resource for biomarker discovery because of its high copy number and increased mutational frequency in cancer cells. We examined if mtDNA mutations can be detected in circulating extracellular vesicles (EVs) of PDAC patients and used for discerning between cancer and non-cancer subjects. A greater yield of circulating EVs (~ 1.4 fold; p = 0.002) was obtained in PDAC patients (n = 20) than non-cancer (NC) individuals (n = 10). PDAC-EVs contained a higher quantity of total DNA (~ 5.5 folds; p = 0.0001) than NC-EVs and had greater enrichment of mtDNA (~ 14.02-fold; p = 0.0001). PDAC-EVs also had higher levels of cardiolipin (a mitochondrial inner-membrane phospholipid), suggestive of their mitochondrial origin. All mtDNA mutations in PDAC-EVs were unique and frequency was remarkably higher. Most mtDNA mutations (41.5%) in PDAC-EVs were in the respiratory complex-I (RCI) (ND1-ND6), followed by the RCIII gene (CYTB; 11.2%). Among the non-coding genes, D-Loop and RNR2 exhibited the most mutations (15.2% each). Altogether, our study establishes, for the first time, that mtDNA mutations can be detected in circulating EVs and potentially serve as a tool for reliable PDAC diagnosis.

Distribution of microbiota in cervical preneoplasia of racially disparate populations

BACKGROUNDS

Microbiome dysbiosis is an important contributing factor in tumor development and thus may be a risk predictor for human malignancies. In the United States, women with Hispanic/Latina (HIS) and African American (AA) background have a higher incidence of cervical cancer and poorer outcomes than Caucasian American (CA) women.

METHODS

Here, we assessed the distribution pattern of microbiota in cervical intraepithelial neoplasia (CIN) lesions obtained from HIS (n = 12), AA (n = 12), and CA (n = 12) women, who were screened for CC risk assessment. We employed a 16S rRNA gene sequencing approach adapted from the NIH-Human Microbiome Project to identify the microbial niche in all CIN lesions (n = 36).

RESULTS

We detected an appreciably decreased abundance of beneficial Lactobacillus in the CIN lesions of the AA and HIS women compared to the CA women. Differential abundance of potentially pathogenic Prevotella, Delftia, Gardnerella, and Fastidiosipila was also evident among the various racial groups. An increased abundance of Micrococcus was also evident in AA and HIS women compared to the CA women. The detection level of Rhizobium was higher among the AA ad CA women compared to the HIS women. In addition to the top 10 microbes, a unique niche of 27 microbes was identified exclusively in women with a histopathological diagnosis of CIN. Among these microbes, a group of 8 microbiota; Rubellimicrobium, Podobacter, Brevibacterium, Paracoccus, Atopobium, Brevundimonous, Comamonous, and Novospingobium was detected only in the CIN lesions obtained from AA and CA women.

CONCLUSIONS

Microbial dysbiosis in the cervical epithelium represented by an increased ratio of potentially pathogenic to beneficial microbes may be associated with increased CC risk disparities. Developing a race-specific reliable panel of microbial markers could be beneficial for CC risk assessment, disease prevention, and/or therapeutic guidance.

Mitochondrial respiratory complexes: Significance in human mitochondrial disorders and cancers

Mitochondria are pivotal organelles that govern cellular energy production through the oxidative phosphorylation system utilizing five respiratory complexes. In addition, mitochondria also contribute to various critical signaling pathways including apoptosis, damage-associated molecular patterns, calcium homeostasis, lipid, and amino acid biosynthesis. Among these diverse functions, the energy generation program oversee by mitochondria represents an immaculate orchestration and functional coordination between the mitochondria and nuclear encoded molecules. Perturbation in this program through respiratory complexes' alteration results in the manifestation of various mitochondrial disorders and malignancy, which is alarmingly becoming evident in the recent literature. Considering the clinical relevance and importance of this emerging medical problem, this review sheds light on the timing and nature of molecular alterations in various respiratory complexes and their functional consequences observed in various mitochondrial disorders and human cancers. Finally, we discussed how this wealth of information could be exploited and tailored to develop respiratory complex targeted personalized therapeutics and biomarkers for better management of various incurable human mitochondrial disorders and cancers.

Abstract 2212: Racially disparate serum levels of inflammatory cytokines, satiety and stress hormones, and exosomal microRNAs in women with or without a breast cancer diagnosis

Breast cancer (BC) is the most common non-cutaneous malignancy and the second leading cause of cancer-related death in American women. Health disparities in incidence and clinical outcome are also reported among different racial groups, most notably African American (AA) women, who are often diagnosed at a young age with aggressive BC and exhibit greater mortality than Caucasian American (CA) women. Since socioeconomic difficulties can have tremendous impact on psychophysiology besides limiting the access to optimal healthcare, we examined the serum levels of stress (cortisol) and satiety (leptin) hormones as well as inflammatory cytokines (resistin and interleukin-6/IL-6) in AA and CA women. To observe a potential epigenomic connection, we also performed profiling of a targeted set of exosomal microRNAs in serum samples. The study was conducted under an Institutional Review Board (IRB) approved protocol. All subjects participated voluntarily, and their consents were obtained. Serum levels of resistin, IL-6, leptin, and cortisol were quantified by Enzyme linked Immunosorbent Assay (ELISA) using commercial kits. Exosomes were isolated using precipitation method and recovered by standard centrifugation. Total RNA was isolated from exosomal preps and subjected to stem-loop RT-PCR for quantitation of a set of inflammation-associated microRNAs. We found that the levels of resistin, leptin, IL-6 and cortisol were higher in women with a BC diagnosis than non-BC subjects. Moreover, AA women with or without BC showed significantly higher levels of these cytokines and hormones in their serum as compared to the CA women with or without a BC diagnosis, respectively. We also observed differential expression of several microRNAs in serum of BC women as compared to their normal counterparts, of which five (miR511, miR33a, miR27a, miR6794, miR143-3p) exhibited highest presence in serum exosomes of AA women with BC. Together, these findings suggest that relatively greater exposure of minority women to social stressors may have epigenomic consequences and may potentially be linked to the observed BC racial health disparities.

Citation Format: Sarabjeet Kour Sudan, Kunwar Somesh Vikramdeo, Amod Sharma, Sachin Kumar Deshmukh, Sanjeev Kumar Srivastava, Teja Poosarla, Nicolette P. Holliday, Donna L. Dyess, Ajay P. Singh, Seema Singh. Racially disparate serum levels of inflammatory cytokines, satiety and stress hormones, and exosomal microRNAs in women with or without a breast cancer diagnosis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2212.

Abstract 1546: Cortisol induces the expression of miR-143-3p/miR-145 cluster in macrophages to affect macrophage polarization via reprogramming of glucose metabolism

Cortisol, the primary stress hormone, can contribute to cancer development through a variety of mechanisms. In a population-based research study, we have detected high serum levels of cortisol and several exosomal microRNAs (miRs) in women with a breast cancer (BC) diagnosis than non-cancer female subjects. In this study, we identified a positive correlation of cortisol levels with an exosomal miRNA, miR-143-3p, in serum samples. Furthermore, we observed an upregulation of miR-143-3p in human monocyte (THP1 and U937)-derived macrophages upon treatment with cortisol but not in BC cell lines (MDA-MB-468 and MDA-MB-231). Enhanced levels of miR-143-3p were also found in exosomes collected from the cortisol-treated macrophages. Expression of miR-145 (transcribed as cluster miRNA with miR-143-3p) was also upregulated in cortisol-treated macrophages but their enhanced levels were not detected in shed exosomes. In silico analysis identified glucocorticoid-response elements (GREs) in the upstream promoter sequence, which exhibited elicited transcriptional activity in response to cortisol in a luciferase-based promoter-reporter assay. Direct binding of glucocorticoid receptor (GR) to the regulatory sequence containing region was confirmed by chromatin immunoprecipitation. We further observed that cortisol treatment inhibited IFN-γ-induced M1 polarization, while caused alternative M2 polarization of macrophages and these effects were inhibited by pre-treatment with miR-143-3p and miR-145 inhibitors. Cortisol treatment reduced ECAR/OCR ratio in macrophages suggesting reduced glycolysis and/or increased oxidative phosphorylation. This effect was neutralized by functional inhibition of miR-143-3p and miR-145. Computational analysis using web-based servers (TargetScan and miRDB) identified HK2 (hexokinase-2) and ADPGK (ADP-dependent glucokinase) as potential targets of miR-143-3p and mir-145, respectively, whose expression was downregulated in cortisol-treated macrophages and rescued upon miR-143-3p and miR-145 inhibition. Direct targeting of 3′- untranslated regions of HK2 and ADPGK by miR-143-3p and miR-145, respectively, was confirmed in luciferase-based reporter assays. Altogether, we have identified novel cortisol-regulated miRNAs that inhibit classical M1 polarization and induce alternative M2 polarization by reprogramming of glucose metabolism. Our findings have relevance in establishing an indirect connection of chronic stress with cancer development via immunosuppressive effect of cortisol, and could be helpful in risk prediction and management efforts.

Citation Format: Amod Sharma, Kunwar Somesh Vikramdeo, Sarabjeet Kour Sudan, Sachin Kumar Deshmukh, Ajay P. Singh, Seema Singh. Cortisol induces the expression of miR-143-3p/miR-145 cluster in macrophages to affect macrophage polarization via reprogramming of glucose metabolism [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1546.

Abstract 2351: MYB plays an essential role in the hypoxic survival of pancreatic cancer cells via its impact on metabolic reprogramming

Pancreatic ductal adenocarcinoma exhibits high degree of intratumoral hypoxia due to its unique histopathological features contributing to its extremely aggressive nature and unusual chemoresistance. It is however not yet very clear what drives and sustains the growth of pancreatic cancer cells under an adverse hypoxic tumor microenvironment. Previously we reported that MYB was overexpressed in pancreatic cancer cells and supported the tumorigenicity and metastatic progression of pancreatic cancer cells. Here, we examined the role of MYB in hypoxic survival of pancreatic cancer cells. We found that the silencing of MYB expression in pancreatic cancer cells severely reduced their growth under hypoxia whereas its forced overexpression promoted hypoxic survival. We also observed that MYB was upregulated under hypoxia and its silencing was associated with a reduced accumulation of hypoxia inducible factor-1 α (HIF1α). Additionally, we confirmed HIF1α as a direct transcriptional target of MYB and its transcripts level and promoter activity correlated positively with MYB expression under both normoxia and hypoxia. Interestingly, restoration of HIF1α expression in MYB-silenced cells was not sufficient to rescue their survival under hypoxia. MYB knockdown pancreatic cancer cells failed to optimally reprogram their metabolism under hypoxia to meet their energetic and biosynthetic demands despite restored HIF1α overexpression. Specifically, MYB knockdown cells exhibited a large decrease in intracellular glucose and several metabolic intermediates of glycolysis, TCA cycle, and amino acid metabolism, whereas glycogenolysis and pentose phosphate pathway metabolites were increased. MYB silencing also altered the expression of several metabolic genes, including established hypoxia-responsive gene targets. MYB co-occupied the promoter regions of GLUT3, HK2, PFKL, ENO2, and MCT4 with HIF1α and its silencing reduced HIF1α binding to these promoters despite its forced overexpression. We also confirmed MYB interaction with HIF1α and p300 and demonstrated enhanced recruitment of p300 to these gene promoters in MYB-overexpressing pancreatic cancer cells. Altogether, our studies suggest that MYB acts as major regulator of metabolic reprogramming and HIF1α signaling and thus acts as an important driver of hypoxic survival of pancreatic cancer cells.

Citation Format: Shashi Anand, Mohammad Aslam Khan, Haseeb Zubair, Sarabjeet Kour Sudan, Kunwar Somesh Vikramdeo, Sachin Kumar Deshmukh, Shafquat Azim, Sanjeev Kumar Srivastava, Seema Singh, Ajay Pratap Singh. MYB plays an essential role in the hypoxic survival of pancreatic cancer cells via its impact on metabolic reprogramming [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 2351.

Platinum-resistant ovarian cancer: From drug resistance mechanisms to liquid biopsy-based biomarkers for disease management

Resistance to platinum-based chemotherapy is a major clinical challenge in ovarian cancer, contributing to the high mortality-to-incidence ratio. Management of the platinum-resistant disease has been difficult due to diverse underlying molecular mechanisms. Over the past several years, research has revealed several novel molecular targets that are being explored as biomarkers for treatment planning and monitoring of response. The therapeutic landscape of ovarian cancer is also rapidly evolving, and alternative therapies are becoming available for the recurrent platinum-resistant disease. This review provides a snapshot of platinum resistance mechanisms and discusses liquid-based biomarkers and their potential utility in effective management of platinum-resistant ovarian cancer.

Hyaluronan-binding protein 1 (HABP1) overexpression triggers induction of senescence in fibroblasts cells

Hyaluronan-binding protein 1 (HABP1), a multi-compartmental, multi-functional protein has a wide range of functions, which can be attributed to its ability to associate with a variety of cellular ligands. Earlier we have reported that HABP1 overexpression in rat normal fibroblasts (F-HABP07) shows chronic generation of reactive oxygen species (ROS), induction of autophagy, and apoptosis. However, a significant proportion of cells remained viable after the majority went through apoptosis from 60 to 72 h. In this study, an attempt has been made to delineate the cellular events in the declined population of surviving cells. It has been elucidated here that, these cells at later time points of growth, that is, 72 and 84 h, not only appeared to shrink but also are devoid of autophagic vacuoles and displayed polyploidy. F-HABP07 cells exhibited an altered cytoskeletal structure from their parental cell line F111, assumed to be caused upon inhibition of actin polymerization and decrease in IQ motif-containing GTPase activating protein 1 (IQGAP1), a key protein associated with maintenance of cytoskeletal integrity. Enhanced expression and nuclear localization of AKT observed in F-HABP07 cells appears to be contributing toward the maintenance of high ROS levels in these cells and also potentially modulating the IQGAP1 activity. These observations, in fact have been considered to result in sustained DNA damage, which then leads to increased expression of p53 and activation of p21 and carry out the cellular events responsible for senescence. Subsequent assessment of the presence of positive β-gal staining and enhanced expression of p16^INK4a in F-HABP07, confirmed that HABP1 overexpressing fibroblasts undergo senescence.

Designing novel inhibitors against histone acetyltransferase (HAT: GCN5) of Plasmodium falciparum

During active proliferation phase of intra-erythrocytic cycle, the genome of P. falciparum is regulated epigenetically and evolutionary conserved parasite-specific histone proteins are extensively acetylated. The reversible process of lysine acetylation, causing transcriptional activation and its deacetylation, causing transcriptional repression is regulated by balanced activities of HATs and HDACs. They are also known to regulate antigenic variations and gametocytic conversion in P. falciparum. These histone modifying enzymes have been identified as potential targets for development of anitmalarials in literature. PfGCN5, a HAT family member of P. falciparum is predominantly involved in H3K9 acetylation. In this study, through comparative structure and sequence analysis, we elucidate differences in the catalytic pocket of PfGCN5 which can be exploited to design selective inhibitors. Through virtual screening of known antimalarials from ChEMBL bioassay database, we mapped 10 compounds with better affinity towards PfGCN5. Further, we identified 10 more novel compounds which showed remarkably better affinity towards the Plasmodium target from analogues of mapped inhibitors from ZINC database of commercially available compounds. Comparative molecular dynamics simulation study of one of the compounds (C14) complex with PfGCN5 and HsGCN5 suggested the possible reason for its selectivity. In vitro parasite growth assay in the presence of C14 showed IC50 value at lower nanomolar range (∼ 225 nM). However, no effect in mammalian fibroblast cells was observed for C14 (up to 20 μM). Further, reduced level of HAT activity of recombinant GCN5 and H3K9Ac was observed in the parasites treated with C14. Overall, this study reports 20 potential inhibitors of PfGCN5 and experimental validation of one molecule (C14) with antimalarial activity at low nanomolar range.

Design, Synthesis and Evaluation of Bifunctional Acridinine-Naphthalenediimide Redox-Active Conjugates as Antimalarials

A novel class of bifunctional molecules was synthesized integrating acridine (Ac) and redox-active naphthalenediimide (NDI) scaffolds directly and through a flexible linker (en). We evaluated in vitro antiplasmodial activity, physicochemical properties, and a possible mode of action. Theoretical studies suggested electronic segmentation between the electron-rich Ac and electron-deficient NDI scaffolds. Orthogonal Ac-NDI molecules showed activities in the micromolar to submicromolar range against a chloroquine (CQ)-sensitive strain of human malaria pathogen Plasmodium falciparum (maximum activity, IC₅₀: 0.419 μM). The flexible Ac-en-NDI molecules were most potent and showed activity in the nanomolar range against both CQ-sensitive (with most effective compounds, IC₅₀: 3.65 and 4.33 nM) as well as CQ-resistant (with most effective compounds, IC₅₀: 52.20 and 28.53 nM) strains of P. falciparum. Significantly, with CQ-resistant strains, the activity of the most effective compounds was 1 order of magnitude better than that of standard drug CQ. Ac-en-NDI-conjugated molecules were significantly more potent than the individual NDI and Ac-based molecules. The structure-activity relationship (SAR) suggests that the flexible spacer (en) linking the Ac and NDI scaffolds plays a vital role in exhibiting improved potency. None of the molecules triggered hemolysis in culture, and the most potent compounds did not show cytotoxicity in vitro against mammalian fibroblast NIH3T3 cells at their respective IC₅₀ values. The other significant outcome of this work is that some of the investigated molecules have the potential to affect multiple processes in the parasite including the hemozoin formation in digestive vacuoles (DVs), mitochondrial membrane potential, and the redox homeostasis of the parasite.