Tankyrase 1 (TNKS) and tankyrase 2 (TNKS2) belong to the poly(ADP-ribose) polymerase family of proteins, which use nicotinamide adenine dinucleotide to modify substrate proteins with ADP-ribose modifications. Emerging evidence has revealed the pathological relevance of TNKS and TNKS2, and identified these two enzymes as potential drug targets. However, the cellular functions and regulatory mechanisms of TNKS/2 are still largely unknown. Through a proteomic analysis, we defined the protein-protein interaction network for human TNKS/2 and revealed more than 100 high-confidence interacting proteins with numerous biological functions in this network. Finally, through functional validation, we uncovered a role for TNKS/2 in peroxisome homeostasis and determined that this function is independent of TNKS enzyme activities. Our proteomic study of the TNKS/2 protein interaction network provides a rich resource for further exploration of tankyrase functions in numerous cellular processes.

The Hippo pathway plays a crucial role in organ size control and tumor suppression, but its precise regulation is not fully understood. In this study, we discovered that phosphatidic acid (PA)-related lipid signaling is a key regulator of the Hippo pathway. Supplementing PA in various Hippo-activating conditions activates YAP. This PA-related lipid signaling is involved in Rho-mediated YAP activation. Mechanistically, PA directly interacts with Hippo components LATS and NF2 to disrupt LATS-MOB1 complex formation and NF2-mediated LATS membrane translocation and activation, respectively. Inhibition of phospholipase D (PLD)-dependent PA production suppresses YAP oncogenic activities. PLD1 is highly expressed in breast cancer and positively correlates with YAP activation, suggesting their pathological relevance in breast cancer development. Taken together, our study not only reveals a role of PLD-PA lipid signaling in regulating the Hippo pathway but also indicates that the PLD-PA-YAP axis is a potential therapeutic target for cancer treatment.

The migrating keratinocyte wound front is required for skin wound closure. Despite significant advances in wound healing research, we do not fully understand the molecular mechanisms that orchestrate collective keratinocyte migration. Here, we show that, in the wound front, the epidermal transcription factor Grainyhead like-3 (GRHL3) mediates decreased expression of the adherens junction protein E-cadherin; this results in relaxed adhesions between suprabasal keratinocytes, thus promoting collective cell migration and wound closure. Wound fronts from mice lacking GRHL3 in epithelial cells (Grhl3-cKO) have lower expression of Fascin-1 (FSCN1), a known negative regulator of E-cadherin. Assay for Transposase-Accessible Chromatin using sequencing (ATAC-seq) on wounded keratinocytes shows decreased wound-induced chromatin accessibility near the Fscn1 gene in Grhl3-cKO mice, a region enriched for GRHL3 motifs. These data reveal a wound-induced GRHL3/FSCN1/E-cadherin pathway that regulates keratinocyte-keratinocyte adhesion during wound-front migration; this pathway is activated in acute human wounds and is altered in diabetic wounds in mice, suggesting translational relevance.

The Hippo pathway, which plays a critical role in organ size control and cancer, features numerous WW domain-based protein-protein interactions. However, ~100 WW domains and 2,000 PY motif-containing peptide ligands are found in the human proteome, raising a "WW-PY" binding specificity issue in the Hippo pathway. In this study, we have established the WW domain binding specificity for Hippo pathway components and uncovered a unique amino acid sequence required for it. By using this criterion, we have identified a WW domain-containing protein, STXBP4, as a negative regulator of YAP. Mechanistically, STXBP4 assembles a protein complex comprising α-catenin and a group of Hippo PY motif-containing components/regulators to inhibit YAP, a process that is regulated by actin cytoskeleton tension. Interestingly, STXBP4 is a potential tumor suppressor for human kidney cancer, whose downregulation is correlated with YAP activation in clear cell renal cell carcinoma. Taken together, our study not only elucidates the WW domain binding specificity for the Hippo pathway, but also reveals STXBP4 as a player in actin cytoskeleton tension-mediated Hippo pathway regulation.