The Fibroblast Code: ANKRD1 Bridges Hormonal Loss to Cancer Progression

Cancer-Associated Fibroblasts (CAFs) are an component of the tumor microenvironment, playing a crucial role in cancer progression, metastasis, and response to therapy. They are a heterogeneous population of activated fibroblasts found within and around solid tumors. Unlike normal fibroblasts, which maintain tissue structure and integrity, CAFs are altered by tumor-derived signals and exhibit a range of pro-tumorigenic functions.  CAFs are in an activated state, characterized by increased proliferation, mobility, and the secretion of various growth factors, cytokines, and extracellular matrix (ECM) components. They express specific markers that distinguish them from normal fibroblasts, such as alpha-smooth muscle actin (α-SMA), fibroblast activation protein (FAP), platelet-derived growth factor receptors (PDGFR-α/β), and vimentin, although none of these markers are exclusively specific to CAFs. Moreover, they can originate from various cell types, including resident fibroblasts, mesenchymal stem cells, endothelial cells (through endothelial-to-mesenchymal transition), and even epithelial cells (via epithelial-to-mesenchymal transition) under the influence of tumor-derived factors. CAFs promote tumor growth by secreting growth factors that directly stimulate tumor cell proliferation and survival. Additionally, CAFs remodel the ECM, contributing to a stiffened tumor microenvironment that enhances tumor cell motility and invasion, facilitating metastasis. By producing pro-angiogenic factors, CAFs stimulate the formation of new blood vessels, supplying the growing tumor with oxygen and nutrients. They can also suppress the immune response against tumors by secreting immunosuppressive molecules and recruiting immunosuppressive cell types, thereby helping tumors evade immune surveillance. Furthermore, they can contribute to the resistance of tumors to various therapies, including chemotherapy, radiotherapy, and targeted therapies, through multiple mechanisms such as creating physical barriers to drug delivery, altering drug metabolism, and inducing survival signaling in tumor cells.

A new study published in Nature Communications and led by Professor Gian Paolo Dotto from Harvard University and Massachusetts General Hospital and performed by Luigi Mazzeo, Soumitra Ghosh, Emery Di Cicco, Jovan Isma, Daniele Tavernari, Anastasia Samarkina, Paola Ostano, Markus K. Youssef, & Christian Simon, authors conducted a detailed investigation into the role of fibroblasts in various pathologies, with a particular focus on their transformation into CAFs during the early stages of cancer development. The study meticulously explored the mechanisms underlying this transformation, highlighting the suppression of fibroblast senescence and CAF activation by the androgen receptor (AR).

The team conducted an in-depth analysis of gene expression profiles in human dermal fibroblasts (HDFs) and CAFs derived from skin squamous cell carcinomas (SCCs) and other cancers. This included examining the effects of AR gene silencing and treatment with the bromodomain and extra terminal protein (BET) inhibitor JQ1, which is known to restore AR expression. Through their analysis, ANKRD1 emerged as a critical gene under direct negative control of AR in HDFs. ANKRD1 was upregulated in CAFs across various cancer types, and its expression was necessary and sufficient for CAF activation, independent of cellular senescence. The researchers demonstrated that ANKRD1 binds to the regulatory regions of my-CAF effector genes alongside AP-1 transcription factors, facilitating the association of c-JUN and FOS within the AP-1 complex. This interaction was crucial for the transcriptional activation of genes associated with CAFs.  The study also explored the therapeutic potential of targeting ANKRD1. By disrupting AP-1 complex formation through ANKRD1 targeting, the team was able to reverse CAF activation and attenuate the pro-tumorigenic properties of CAFs in a skin cancer model.

They authors identified ANKRD1 as a mesenchymal-specific transcriptional coregulator, driving the conversion of fibroblasts to CAFs by bridging the loss of AR to AP-1 activation. This conversion was shown to occur independently of cellular senescence, positioning ANKRD1 as a pivotal factor in CAF activation. They found the expression of ANKRD1 in CAFs to be correlated with poor survival rates in patients with head and neck squamous cell carcinoma (HNSCC), lung, and cervical SCC, underscoring the clinical relevance of ANKRD1 in cancer progression. The ability to reverse CAF activation by targeting ANKRD1 highlights its potential as a therapeutic target. The study suggests that disrupting the ANKRD1-AP-1 axis could offer a novel strategy for fibroblast-directed therapy in cancer and possibly other fibroblast-related diseases.

One key findings of the study is it highlighted the role of fibroblast senescence and the transformation into tumor-promoting CAFs, which are usually suppressed by the AR. The identification of ANKRD1 as a driver of CAF conversion independent of cellular senescence opens new avenues for targeting fibroblast activation in cancer. ANKRD1’s expression in CAFs is associated with poor survival in several cancers, and it regulates a specific gene expression program in myofibroblast CAFs, promoting c-JUN and FOS association within the AP-1 transcription factor complex. The research provides insight into the negative regulation of ANKRD1 by AR in human dermal fibroblasts (HDFs) and establishes ANKRD1 as a necessary and sufficient factor for CAF activation. This is supported by the finding that targeting ANKRD1 disrupts AP-1 complex formation, reverses CAF activation, and blocks the pro-tumorigenic properties of CAFs in a skin cancer model. These findings position ANKRD1 as a potential target for therapy not only in cancer but possibly in other fibroblast-related pathologies. The study also explores the implications of UVA exposure in skin aging and cancer, highlighting the direct targeting of dermal cells and suppression of critical regulators like AR and CSL, leading to cellular senescence and CAF activation. The detailed analysis of global transcriptomic profiles and the functional significance of elevated ANKRD1 expression in CAFs, coupled with the demonstration of ANKRD1’s direct binding to my-CAF effector genes, underscores the translational relevance of these findings.

In conclusion, Professor Gian Paolo Dotto and his colleagues identified the complexity of the tumor microenvironment and the critical role of fibroblasts in cancer progression. By elucidating the molecular mechanisms underlying CAF activation, particularly the role of ANKRD1 and its interaction with the AP-1 complex, this study provides valuable insights into potential therapeutic targets and strategies for combating cancer and other diseases involving fibroblast pathology.