Gap junctions mediate glucose transfer to promote colon cancer growth in three-dimensional spheroid culture.

In vivo tumor growth is characterized by a necrotic core generated by oxygen and nutrients gradients, which is replicated by in vitro three-dimensional (3D) tumor spheroids but not traditional two-dimensional cell monolayers. Gap junctions provide direct communication between adjacent cells and play a critical role in cancer development, but their effects are still debatable. In this study, we found that connexin 43 (Cx43) reduced the area of necrotic core in colon cancer 3D spheroids, thus providing a growth advantage. This impact is dependent on gap junction channel functions, as the channel blocker carbenoxolone or connexin channel death mutant reverses this effect. Additionally, enhanced glucose uptake was detected in Cx43-overexpressing spheroids, along with upregulated mTOR, downregulated AMPK signaling, increased ATP content, and enhanced oxygen consumption rate. Furthermore, the xenograft mouse model confirmed the growth advantage of Cx43 in vivo. RNAseq data and clinical information from The Cancer Genome Atlas (TCGA) database indicated a more heterogeneous expression pattern of Cx43 in colon cancer compared to normal colon tissue, and higher Cx43 level is associated with worse clinical outcomes. Our data suggest a novel function of connexin in tumor growth, that gap junctions may provide nutrients transmitting routes in lieu of vasculature to meet the increasing metabolic requirement of solid tumors.

Deregulation of Exo70 Facilitates Innate and Acquired Cisplatin Resistance in Epithelial Ovarian Cancer by Promoting Cisplatin Efflux.

Whilst researches elucidating a diversity of intracellular mechanisms, platinum-resistant epithelial ovarian cancer (EOC) remains a major challenge in the treatment of ovarian cancer. Here we report that Exo70, a key subunit of the exocyst complex, contributes to both innate and acquired cisplatin resistance of EOC. Upregulation of Exo70 is observed in EOC tissues and is related to platinum resistance and progression-free survival of EOC patients. Exo70 suppressed the cisplatin sensitivity of EOC cells through promoting exocytosis-mediated efflux of cisplatin. Moreover, cisplatin-induced autophagy-lysosomal degradation of Exo70 protein by modulating phosphorylation of AMPK and mTOR, thereby reducing the cellular resistance. However, the function was hampered during prolonged cisplatin treatment, which in turn stabilized Exo70 to facilitate the acquired cisplatin resistance of EOC cells. Knockdown of Exo70, or inhibiting exocytosis by Exo70 inhibitor Endosidin2, reversed the cisplatin resistance of EOC cells both in vitro and in vivo. Our results suggest that Exo70 overexpression and excessive stability contribute to innate and acquired cisplatin resistance through the increase in cisplatin efflux, and targeting Exo70 might be an approach to overcome cisplatin resistance in EOC treatment.

The HNF4α-BC200-FMR1-Positive Feedback Loop Promotes Growth and Metastasis in Invasive Mucinous Lung Adenocarcinoma.

Invasive mucinous lung adenocarcinoma (IMA) is a subtype of lung adenocarcinoma with a strong invasive ability. IMA frequently carries "undruggable" KRAS mutations, highlighting the need for new molecular targets and therapies. Nuclear receptor HNF4α is abnormally enriched in IMA, but the potential of HNF4α to be a therapeutic target for IMA remains unknown. Here, we report that P2 promoter-driven HNF4α expression promotes IMA growth and metastasis. Mechanistically, HNF4α transactivated lncRNA BC200, which acted as a scaffold for mRNA binding protein FMR1. BC200 promoted the ability of FMR1 to bind and regulate stability of cancer-related mRNAs and HNF4α mRNA, forming a positive feedback circuit. Mycophenolic acid, the active metabolite of FDA-approved drug mycophenolate mofetil, was identified as an HNF4α antagonist exhibiting anti-IMA activities in vitro and in vivo. This study reveals the role of a HNF4α-BC200-FMR1-positive feedback loop in promoting mRNA stability during IMA progression and metastasis, providing a targeted therapeutic strategy for IMA. SIGNIFICANCE: Growth and metastatic progression of invasive mucinous lung adenocarcinoma can be restricted by targeting HNF4α, a critical regulator of a BC200-FMR1-mRNA stability axis.

Structure-Activity Relationship Study Enables the Discovery of a Novel Berberine Analogue as the RXRα Activator to Inhibit Colon Cancer.

We reported recently that berberine (Ber), a traditional oriental medicine to treat gastroenteritis, binds and activates retinoid X receptor α (RXRα) for suppressing the growth of colon cancer cells. Here, we extended our studies based on the binding mode of Ber with RXRα by design, synthesis, and biological evaluation of a focused library of 15 novel Ber analogues. Among them, 3,9-dimethoxy-5,6-dihydroisoquinolino[3,2-a]isoquinolin-7-ium chloride (B-12) was identified as the optimal RXRα activator. More efficiently than Ber, B-12 bound and altered the conformation of RXRα/LBD, thereby suppressing the Wnt/ß-catenin pathway and colon cancer cell growth via RXRα mediation. In addition, B-12 not only preserved Ber's tumor selectivity but also greatly improved its bioavailability. Remarkably, in mice, B-12 did not show obvious side effects including hypertriglyceridemia as other RXRα agonists or induce hepatorenal toxicity. Together, our study describes an approach for the rational design of Ber-derived RXRα activators as novel effective antineoplastic agents for colon cancer.

ULK1 phosphorylates Exo70 to suppress breast cancer metastasis.

Increased expression of protein kinase ULK1 was reported to negatively correlate with breast cancer metastasis. Here we report that ULK1 suppresses the migration and invasion of human breast cancer cells. The suppressive effect is mediated through direct phosphorylation of Exo70, a key component of the exocyst complex. ULK1 phosphorylation inhibits Exo70 homo-oligomerization as well as its assembly to the exocyst complex, which are needed for cell protrusion formation and matrix metalloproteinases secretion during cell invasion. Reversely, upon growth factor stimulation, Exo70 is phosphorylated by ERK1/2, which in turn suppresses its phosphorylation by ULK1. Together, our study identifies Exo70 as a substrate of ULK1 that inhibits cancer metastasis, and demonstrates that two counteractive regulatory mechanisms are well orchestrated during tumor cell invasion.

Matrine Reverses the Warburg Effect and Suppresses Colon Cancer Cell Growth via Negatively Regulating HIF-1α.

The Warburg effect is a peculiar feature of cancer's metabolism, which is an attractive therapeutic target that could aim tumor cells while sparing normal tissue. Matrine is an alkaloid extracted from the herb root of a traditional Chinese medicine, Sophora flavescens Ait. Matrine has been reported to have selective cytotoxicity toward cancer cells but with elusive mechanisms. Here, we reported that matrine was able to reverse the Warburg effect (inhibiting glucose uptake and lactate production) and suppress the growth of human colon cancer cells in vitro and in vivo. Mechanistically, we revealed that matrine significantly decreased the messenger RNA (mRNA) and protein expression of HIF-1α, a critical transcription factor in reprogramming cancer metabolism toward the Warburg effect. As a result, the expression levels of GLUT1, HK2, and LDHA, the downstream targets of HIF-1α in regulating glucose metabolism, were dramatically inhibited by matrine. Moreover, this inhibitory effect of matrine was significantly attenuated when HIF-1α was knocked down or exogenous overexpressed in colon cancer cells. Together, our results revealed that matrine inhibits colon cancer cell growth via suppression of HIF-1α expression and its downstream regulation of Warburg effect. Matrine could be further developed as an antitumor agent targeting the HIF-1α-mediated Warburg effect for colon cancer treatment.