Tatiana V. Kudryashova, PhD, from the University of Pittsburgh.

Tatiana V. Kudryashova, PhD

2026 American Thoracic Society (ATS) International Conference 

in Orlando, Florida, investigators presented findings evaluating the role of E2F transcription factor 2 (E2F2) in pulmonary arterial smooth muscle cell (PASMC) proliferation in 

. The study focused on identifying signaling pathways downstream of homeodomain-interacting protein kinase-2 (HIPK2), a transcriptional coregulator previously associated with pro-proliferative and pro-survival signaling in PAH PASMCs.

Using RNA sequencing analysis of PAH PASMCs treated with the HIPK2 inhibitor tBID, investigators identified downregulation of several transcription factors, including MYBL2 and E2F2, with only E2F2 also demonstrating reduced protein expression on immunoblot analysis. Additional analyses using publicly available datasets and primary PASMC samples from patients with PAH showed increased E2F2 expression at both the mRNA and protein levels compared with non-diseased controls. Investigators also identified increased expression of TFDP1, a known binding partner of E2F2 involved in cell-cycle progression and growth-related gene activation.

The investigators further evaluated potential mechanisms regulating E2F2 expression and reported that E2F2 upregulation appeared independent of AKT kinase and YAP signaling pathways in siRNA- and inhibitor-based studies. Functional analyses demonstrated that siRNA-mediated downregulation of E2F2 significantly reduced proliferation in hyperproliferative PAH PASMCs as measured by BrdU incorporation. In this Q&A, Tatiana V. Kudryashova, PhD, from the University of Pittsburgh, discussed the study findings, the significance of E2F2 signaling in PAH, and future directions for evaluating anti-remodeling therapeutic approaches targeting proliferative pathways in the disease.

 Your work identifies E2F2 as upregulated in PAH smooth muscle cells. How central do you think this pathway is to the broader proliferative phenotype seen in pulmonary arterial hypertension?

 Besides PAH smooth muscle cells, we found a significant increase in E2F2 on both mRNA and protein levels. We also analyzed the expression of the E2F2 gene on other vascular cell types—endothelial cells and fibroblasts—using publicly available transcriptomic data sets. We didn't detect any obvious changes in E2F2 expression in pH compared to non-diseased cells. Of course, these transcriptomic findings require further validation on the protein level to confirm E2F2 functional relevance in PH pathobiology.

 E2F2 is a well-known regulator of G1-to-S phase progression. What makes it an attractive target compared with other cell-cycle regulators that have been explored in PAH?

The key [G1-to-S] regulators include cyclin D, CDK4 and 6, cyclin E, CDK2, RB, a family of E2F2 factors, and CDK inhibitors. It was well demonstrated that the CDK axis is indeed dysregulated in pH smooth muscle cells, and it has been directly studied in this context.

All current approaches either cause significant toxicity or fail to show clinical benefits in reversing the established vascular remodeling that drives pH progression. Unlike broad CDK inhibitors, E2F2 sits downstream in the pathway, potentially allowing more precise targeting of an abnormal vascular cell proliferation with fewer systemic side effects.

E2F2 may be more selectively [active] in PH smooth muscle cells, meaning targeting it could [better suppress] proliferative [programming], driving vascular remodeling more specifically than current approaches. Since E2F2 is an unexplored target in pH, it also offers a novel therapeutic angle that previously has not been addressed.

 You also showed that E2F2 knockdown reduced PASMC proliferation. How do you interpret the strength of that functional signal in terms of therapeutic potential?

We are at the early stage of discovery and in vitro stages of our studies. It's important to be both encouraged and appropriately cautious about functional effects. A strong anti-proliferative effect, which we detected in a cell-based system, tells us that we have genuine biological activity, that the target is engaged, and the pathway is responsive.

We interpret this data more as a proof-of-concept rather than a direct predictor of therapeutic outcomes, and the key questions we want to answer next [include]: Does this effect hold across multiple cell lines, and is the specific targeting of E2F2 physiologically achievable? How does it behave under more complex or stress conditions?

Overall, [the] positive in vitro [functional] effect, which we observed at this stage, supports its potential attractiveness as a target. Therapeutic potential ultimately depends on multiple other factors, which need to be further investigated.

 HIPK2 appears to regulate E2F2, but your data suggest this is independent of AKT and YAP signaling. Why is that independence important biologically or therapeutically?

YAP and AKT are well-established drivers of smooth muscle cell proliferation, apoptosis resistance in PH, and progressive vascular remodeling. However, [completely] inhibiting either target presents therapeutic challenges.

AKT plays essential roles in glucose homeostasis and cardiac survival signaling, [and its inhibition can lead to] toxicities, including hyperglycemia, cardiac dysfunction, and QT prolongation. YAP is equally indispensable [and] critical for normal tissue homeostasis, organ repair, and regeneration.

A more rational strategy is to simultaneously partially inhibit multiple independent pathways at subtherapeutic doses. In this approach, the synergetic efficacy is achieved without the toxicity of complete single-target blockade. It offers a mechanistically distinct node that could be incorporated into such a combination strategy and potentially improves therapeutic efficacy while maintaining an acceptable safety profile for pH patients.

 From a translational perspective, what are the biggest challenges in moving a target like E2F2 from mechanistic biology into a druggable pathway in PAH?

Transcriptional factors have historically been considered undruggable targets. However, recent advances offer genuine hope. Direct TF transcription factors inhibition has now been validated clinically, at least for heath 2f alpha and STAT3 inhibitor, which is entering phase 1 clinical trials. This demonstrates that transcription factors can be selectively targeted and provide a roadmap for targeting E2F2.

The second challenge is that E2F2 belongs to a functional and structurally related subgroup [that includes E2F1 and E2F3]. They share similar domain structures, overlapping target genes, and RB-dependent regulation. [The] loss of all 3 together leads to profound cell cycle arrest. This raises the concern that selective E2F2 inhibition may have limited therapeutic impact if E2F1 and if E2F3 can functionally substitute [for] each other and E2F2.

 Do you think E2F2 is more likely to serve as a direct therapeutic target, or as a biomarker of proliferative disease activity in pulmonary vascular remodeling?

It has [the] potential to be considered a therapeutic target. Using it as a biomarker is more challenging since it is a transcription factor [with] nuclear localization. No data indicate that it can be excreted and measured as a circulating biomarker.

However, we can't exclude the possibility that E2F2-related noncoding RNAs or mRNAs could potentially be detected in circulating extracellular vesicles or exosomes. This, of course, required further investigation.

 What is the next critical step to validate this pathway in vivo or in human disease before it could influence PAH treatment strategies?

We're also planning to evaluate the in vitro effects of E2F2 downregulation in non-diseased PA smooth muscle cells since we're hoping that downregulation of E2F2 [will] have detrimental effects only in diseased cells. By this, we hope to reduce systemic toxicity, minimize the potential of target effects and other cell types, and overall improve the safety profile of this new novel therapeutic strategy.

) E2F Transcription Factor 2 (E2F2) Supports Increased Proliferation in Pulmonary Arterial Smooth Muscle Cells in Pulmonary Arterial Hypertension. Late breaker presented at ATS 2026 in Orlando, Florida, on May 20.


Articles

In this Q&A, Tatiana V. Kudryashova, PhD, discusses new data presented at ATS 2026 that show silencing E2F2 suppresses hyperproliferation in PAH smooth muscle cells.