The TBX2 subfamily of T-box transcription factors (e.g., Tbx2, Tbx3, Tbx4, Tbx5) plays an essential role in lung development. Down-regulation of these genes in human lung adenocarcinoma suggests that these genes may be tumor-suppressive; however, because down-regulation appears to occur primarily via epigenetic change, it remains unclear if these changes causally drive tumor progression or are merely the consequence of upstream events. Herein, we developed the first multiplexed mouse model to study the impact of TBX2 subfamily loss, alongside associated signaling genes (Egr1, Chd2, Tnfaip3a, and Atf3) in Ras-driven lung cancer. Using tumor-barcoding with high-throughput barcode sequencing (TuBa-seq), a high-throughput tumor-barcoding system, we quantified the growth effects of these knockouts during early and late tumorigenesis. Chd2 knockout suppressed both tumor initiation and progression, whereas Tnfaip3 knockout enhanced tumor initiation and overall tumor growth. Tbx2 loss showed stage-specific effects on tumor development. Notably, Egr1 emerged as a strong tumor suppressor and its knockout resulted in approximately a fivefold increase in tumor size at 20 weeks (two-sample t-test, p < 0.05), exceeding the impact observed with Rb1 loss. Transcriptomic analyses of Egr1-deficient tumors suggested immune dysregulation, including heightened inflammation and potential markers of Tcell exhaustion in the tumor microenvironment. These findings indicate that Egr1 may play a role in suppressing tumor growth through modulating immune dynamics, offering new insights into the interplay between tumor progression and immune regulation in lung adenocarcinoma.

Phosphoinositide 3-kinases (PI3Ks) are heterodimers consisting of a p110 catalytic subunit and a p85 regulatory subunit. The PIK3CA gene, which encodes the p110α, is the most frequently mutated oncogene in cancer. Oncogenic PIK3CA mutations activate the PI3K pathway, promote tumor initiation and development, and mediate resistance to anti-tumor treatments, making the mutant p110α an excellent target for cancer therapy. PIK3CA mutations occur in two hotspot regions: one in the helical domain and the other in the kinase domain. The PIK3CA helical and kinase domain mutations exert their oncogenic function through distinct mechanisms. For example, helical domain mutations of p110α gained direct interaction with insulin receptor substrate 1 (IRS-1) to activate the downstream signaling pathways. Moreover, p85β proteins disassociate from helical domain mutant p110α, translocate into the nucleus, and stabilize enhancer of zeste homolog 1/2 (EZH1/2). Due to the fundamental role of PI3Kα in tumor initiation and development, PI3Kα-specific inhibitors, represented by FDA-approved alpelisib, have developed rapidly in recent decades. However, side effects, including on-target side effects such as hyperglycemia, restrict the maximum dose and thus clinical efficacy of alpelisib. Therefore, developing p110α mutant-specific inhibitors to circumvent on-target side effects becomes a new direction for targeting PIK3CA mutant cancers. In this review, we briefly introduce the function of the PI3K pathway and discuss how PIK3CA mutations rewire cell signaling, metabolism, and tumor microenvironment, as well as therapeutic strategies under development to treat patients with tumors harboring a PIK3CA mutation.

How PD-L1 expression is regulated in cancer is poorly understood. Here, we report that the ATP-binding activity of ERBB3 pseudokinase regulates PD-L1 gene expression in colorectal cancers (CRCs). ERBB3 is one of the four members of the EGF receptor family, all with protein tyrosine kinase domains. ERBB3 is a pseudokinase with a high binding affinity to ATP. We showed that ERBB3 ATP-binding inactivation mutant reduces tumorigenicity in genetically engineered mouse models and impairs xenograft tumor growth of CRC cell lines. The ERBB3 ATP-binding mutant cells dramatically reduce IFN-γ-induced PD-L1 expression. Mechanistically, ERBB3 regulates IFN-γ-induced PD-L1 expression through the IRS1-PI3K-PDK1-RSK-CREB signaling axis. CREB is the transcription factor that regulates PD-L1 gene expression in CRC cells. Knockin of a tumor-derived ERBB3 mutation located in the kinase domain sensitizes mouse colon cancers to anti-PD1 antibody therapy, suggesting that ERBB3 mutations could be predictive biomarkers for tumors amenable to immune checkpoint therapy.

We recently reported that PIK3CA mutant colorectal cancers (CRCs) are addicted to glutamine through up-regulation of glutamate pyruvate transaminase 2 (GPT2). A GPT2 inhibitor suppresses in vivo growth of PIK3CA mutant, but not wild-type, CRCs. This study indicates that targeting glutamine may be an effective approach to treat CRCs with PIK3CA mutations.