Chronic inflammatory conditions are the primary cause of disease-related mortality worldwide and are characterized by an abnormal expansion of myeloid cells, such as macrophages, fostering a dysregulated immune response. Additionally, many of these inflammatory conditions such as cancer often develop drug resistance, rendering the current available treatments ineffective. Thus, there is an imperative need to identify molecular mechanisms aimed at restoring immune homeostasis and combating resistance during inflammation. Plant-based compounds have gained significant interest in recent years owing to their bioactive and health-beneficial attributes. Among them, flavone apigenin, abundantly found in celery and parsley, has both anti-carcinogenic and immune-modulatory properties. Our group previously found that apigenin binds with high affinity to RNA binding protein heterogeneous nuclear ribonucleoprotein (hnRNP)-A2. HnRNPA2 is known to promote tumor progression. While the role of hnRNPA2 has been the center of several studies, its function in macrophage immune response remains poorly understood. The goal of this dissertation was to study the molecular mechanisms by which hnRNPA2 regulates cancer resistance and macrophage immune function. Because hnRNPA2 is a splicing factor, we sought to investigate if apigenin affects transcriptome-wide alternative splicing (AS) in cancer. We found that apigenin reprograms triple-negative breast cancer (TNBC) associated AS transcriptome-wide by preferentially affecting the splicing of anti-apoptotic and proliferation factors, thereby hindering tumor proliferation. The AS events affected by apigenin were enriched in hnRNPA2 substrates. Apigenin reprogrammed cancer-associated AS isoforms to those found in non-tumor tissues, thereby providing a favorable switch to suppress tumor growth. To study the role of hnRNPA2 in cancer chemoresistance, we established 3-dimensional tumor cultures and evaluated the effect of apigenin through hnRNPA2 on chemo-sensitizing TNBC. Apigenin by targeting hnRNPA2 sensitized spheroids to doxorubicin-induced DNA damage, leading to caspase-9-mediated intrinsic apoptotic pathway. Deletion of hnRNPA2 suppressed apigenin-induced sensitivity to chemotherapeutic drug doxorubicin in TNBC spheroids by decreasing apoptosis while partially reversing apigenin-dependent inhibition of drug-efflux transporters. To investigate the mechanisms underlying the immune-modulatory role of hnRNPA2, we generated hnRNPA2 knockout immortalized bone marrow-derived macrophage (iBMDM) cell lines. We found that hnRNPA2 is an activator of transcription factor NF-κB, a key regulator of cell survival and inflammation. Comparative RNAseq analyses revealed that hnRNPA2-regulated genes are enriched in the inflammatory response and are majorly modulated by NF-κB. Loss of hnRNPA2 suppressed NF-κB transcription activity and subsequent steady-state mRNA and protein expression of inflammatory cytokines in stimulated macrophages. Notably, hnRNPA2 directly associates with NF-κB subunit p65 and functions as its coactivator during inflammation. Taken together, this thesis provides novel insights into the critical role of hnRNPA2 in tumor growth, chemoresistance and macrophage immune regulation, thereby contributing significantly to advancing our understanding of its biological functions and impact on disease progression. Additionally, this thesis provides a fundamental understanding of the mechanisms by which a plant phytochemical such as apigenin exerts its health-beneficial effects, thereby paving the way for the incorporation of nutraceuticals in future treatment regimens for inflammatory diseases.
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