Linda Shyue Huey Chuang

RUNX3 Attenuates β-Catenin/T Cell Factors in Intestinal Tumorigenesis

In intestinal epithelial cells, inactivation of APC, a key regulator of the Wnt pathway, activates beta-catenin to initiate tumorigenesis. However, other alterations may be involved in intestinal tumorigenesis. Here we found that RUNX3, a gastric tumor suppressor, forms a ternary complex with beta-catenin/TCF4 and attenuates Wnt signaling activity. A significant fraction of human sporadic colorectal adenomas and Runx3(+/-) mouse intestinal adenomas showed inactivation of RUNX3 without apparent beta-catenin accumulation, indicating that RUNX3 inactivation independently induces intestinal adenomas. In human colon cancers, RUNX3 is frequently inactivated with concomitant beta-catenin accumulation, suggesting that adenomas induced by inactivation of RUNX3 may progress to malignancy. Taken together, these data demonstrate that RUNX3 functions as a tumor suppressor by attenuating Wnt signaling.

The RUNX family: developmental regulators in cancer

RUNX proteins belong to a family of metazoan transcription factors that serve as master regulators of development. They are frequently deregulated in human cancers, indicating a prominent and, at times, paradoxical role in cancer pathogenesis. The contextual cues that direct RUNX function represent a fast-growing field in cancer research and could provide insights that are applicable to early cancer detection and treatment. This Review describes how RUNX proteins communicate with key signalling pathways during the multistep progression to malignancy; in particular, we highlight the emerging partnership of RUNX with p53 in cancer suppression.

RUNX family: Regulation and diversification of roles through interacting proteins.

The Runt‐related transcription factors (RUNX) belong to an ancient family of metazoan genes involved in developmental processes. Through multiple protein‐interacting partners, RUNX proteins have been implicated in diverse signaling pathways and cellular processes. The frequent inactivation of RUNX genes in cancer indicates crucial roles for RUNX in tumor suppression. This review discusses the abilities of RUNX proteins, in particular RUNX3, to integrate oncogenic signals or environmental cues and to initiate appropriate tumor suppressive responses.

Runx3 Inactivation Is a Crucial Early Event in the Development of Lung Adenocarcinoma

Targeted inactivation of Runx3 in mouse lung induced mucinous and nonmucinous adenomas and markedly shortened latency of adenocarcinoma formation induced by oncogenic K-Ras. RUNX3 was frequently inactivated in K-RAS mutated human lung adenocarcinomas. A functional genetic screen of a fly mutant library and molecular analysis in cultured cell lines revealed that Runx3 forms a complex with BRD2 in a K-Ras-dependent manner in the early phase of the cell cycle; this complex induces expression of p14(ARF)/p19(Arf) and p21(WAF/CIP). When K-Ras was constitutively activated, the Runx3-BRD2 complex was stably maintained and expression of both p14(ARF) and p21(WAF/CIP) was prolonged. These results provide a missing link between oncogenic K-Ras and the p14(ARF)-p53 pathway, and may explain how cells defend against oncogenic K-Ras.

Loss of Runx3 Is a Key Event in Inducing Precancerous State of the Stomach

BACKGROUND & AIMS RUNX3 is a tumor suppressor originally identified in gastric cancer. The mutation R122C in RUNX3 promotes gastric carcinogenesis by unclear mechanisms. We investigated how Runx3-deficiency contributes to distinct changes in the gastric epithelium that precede neoplasia. METHODS Runx3-deficient (Runx3(-/-)) and wild-type BALB/c adult mice were subjected to histological analyses. Gastric cancer formation after administration of N-methyl-N-nitrosourea was evaluated. Runx3(+/+) and Runx3(-/-) gastric epithelial cell lines were used to investigate the molecular basis underlying Runx3 function. RESULTS The gastric epithelia in Runx3(-)/(-) adult mice was hyperplastic, with loss of chief cells and development of mucin 6- and trefoil factor-2-expressing metaplasia. The gastric epithelium of Runx3(-)/(-) mice had an intestinal phenotype that expressed Cdx2. After addition of N-methyl-N-nitrosourea, Runx3- mice, unlike wild-type mice, consistently developed adenocarcinomas, indicating that Runx3-deficiency leads to premalignant changes in the gastric epithelia. RUNX3, but not the RUNX3 mutant R122C, repressed Cdx2 expression by attenuation of oncogenic beta(symbol)-catenin and Tcfs. CONCLUSIONS Runx3-deficiency leads to a precancerous state in the gastric epithelia of mice, characterized by loss of chief cells but not parietal cells; inflammation did not appear to be involved.

RUNX3 functions as an oncogene in ovarian cancer

OBJECTIVE The Runt domain transcription factor, RUNX3, has been shown to be a tumor suppressor in a variety of cancers including gastric, colon and breast cancer. Interestingly, an oncogenic role for RUNX3 has also been suggested in basal cell carcinoma and head and neck cancer. Here, we explore the role of RUNX3 in ovarian cancer. METHODS Expression of RUNX3 mRNA and protein was evaluated in human ovarian cancer cell lines. In addition, subcellular localization of RUNX3 was also examined in cell lines and ovarian cancer tissues. Effect of exogenous RUNX3 expression and knockdown on cell proliferation was investigated by proliferation assays and a soft agar assay. RESULTS Expression of RUNX3 was detected in the nucleus of ovarian cancer cell lines and ovarian cancer tissues and was found to play a growth stimulatory role. RUNX3 knockdown resulted in a decrease in cell proliferation in liquid media as well as in soft agar. Despite the fact that exogenous expression of RUNX3 strongly inhibits cell growth in many cell types, RUNX3 promoted cell growth in ovarian cancer cell lines not expressing RUNX3. CONCLUSION RUNX3 is frequently expressed in the nuclei of ovarian cancer cell lines and plays an oncogenic role in ovarian cancer.

RUNX3 interactome reveals novel centrosomal targeting of RUNX family of transcription factors

RUNX family proteins are critical regulators of lineage differentiation during development. The high prevalence of RUNX mutation/epigenetic inactivation in human cancer indicates a causative role for dysfunctional RUNX in carcinogenesis. This is supported by well-documented evidence of functional interaction of RUNX with components of major oncogenic or tumor suppressive signaling pathways such as TGFβ and Wnt. Here, we explore the binding partners of RUNX3 proteins to further define the scope of RUNX3 function. Using a mass spectrometry-based approach, we found that RUNX3 binds to centrosomal protein rootletin. This led us to uncover the presence of RUNX proteins at the centrosome. Our findings suggest a potential function for RUNX3 during mitosis.

Aurora kinase-induced phosphorylation excludes transcription factor RUNX from the chromatin to facilitate proper mitotic progression

Significance The Runt-related transcription factors (RUNX) are critical regulators of development. Mutation or dysregulation of RUNX genes have been associated with diverse cancer types. Phosphorylation of the strictly conserved threonine 173 (T173) residue within the Runt domain of RUNX3 disrupts DNA binding activity, which facilitates the recruitment of RUNX proteins to mitotic structures. Moreover, RUNX3 deficiency is associated with delayed mitotic entry. The tight conservation of T173 and its flanking residues from unicellular organism to human, and the fact that mitosis is indispensable to all metazoans, strongly indicate that T173 phosphorylation is fundamental to the role of RUNX in these divergent organisms. Cancer-associated mutation T173I further corroborates the critical role of RUNX phosphorylation in mitosis. The Runt-related transcription factors (RUNX) are master regulators of development and major players in tumorigenesis. Interestingly, unlike most transcription factors, RUNX proteins are detected on the mitotic chromatin and apparatus, suggesting that they are functionally active in mitosis. Here, we identify key sites of RUNX phosphorylation in mitosis. We show that the phosphorylation of threonine 173 (T173) residue within the Runt domain of RUNX3 disrupts RUNX DNA binding activity during mitotic entry to facilitate the recruitment of RUNX proteins to mitotic structures. Moreover, knockdown of RUNX3 delays mitotic entry. RUNX3 phosphorylation is therefore a regulatory mechanism for mitotic entry. Cancer-associated mutations of RUNX3 T173 and its equivalent in RUNX1 further corroborate the role of RUNX phosphorylation in regulating proper mitotic progression and genomic integrity.

TGFβ Promotes Genomic Instability after Loss of RUNX3

Studies of genomic instability have historically focused on intrinsic mechanisms rather than extrinsic mechanisms based in the tumor microenvironment (TME). TGFβ is the most abundantly secreted cytokine in the TME, where it imparts various aggressive characteristics including invasive migration, drug resistance, and epithelial-to-mesenchymal transition (EMT). Here we show that TGFβ also promotes genomic instability in the form of DNA double strand breaks (DSB) in cancer cells that lack the tumor suppressor gene RUNX3 Loss of RUNX3 resulted in transcriptional downregulation of the redox regulator heme oxygenase-1 (HO-1 or HMOX1). Consequently, elevated oxidative DNA damage disrupted genomic integrity and triggered cellular senescence, which was accompanied by tumor-promoting inflammatory cytokine expression and acquisition of the senescence-associated secretory phenotype (SASP). Recapitulating the above findings, tumors harboring a TGFβ gene expression signature and RUNX3 loss exhibited higher levels of genomic instability. In summary, RUNX3 creates an effective barrier against further TGFβ-dependent tumor progression by preventing genomic instability. These data suggest a novel cooperation between cancer cell-extrinsic TGFβ signaling and cancer cell-intrinsic RUNX3 inactivation as aggravating factors for genomic instability.Significance: RUNX3 inactivation in cancer removes an antioxidant barrier against DNA double strand breaks induced by TGFβ expressed in the tumor microenvironment. Cancer Res; 78(1); 88-102. ©2017 AACR.

Roles of RUNX in Solid Tumors

All RUNX genes have been implicated in the development of solid tumors, but the role each RUNX gene plays in the different tumor types is complicated by multiple interactions with major signaling pathways and tumor heterogeneity. Moreover, for a given tissue type, the specific role of each RUNX protein is distinct at different stages of differentiation. A regulatory function for RUNX in tissue stem cells points sharply to a causal effect in tumorigenesis. Understanding how RUNX dysregulation in cancer impinges on normal biological processes is important for identifying the molecular mechanisms that lead to malignancy. It will also indicate whether restoration of proper RUNX function to redirect cell fate is a feasible treatment for cancer. With the recent advances in RUNX research, it is time to revisit the many mechanisms/pathways that RUNX engage to regulate cell fate and decide whether cells proliferate, differentiate or die.