The authors measured circulating levels of prohaptoglobin (proHp) in patients with pancreatic cancer and in healthy control individuals. Serum proHp was reported as significantly elevated in the pancreatic cancer group, supporting the idea that proHp may serve as a disease-associated biomarker. The study emphasizes that, beyond systemic production, a subset of pancreatic tumors can act as a source of proHp.
Transcriptomic dataset analyses revealed that some pancreatic tumors and pancreatic cancer cell lines express HP at levels comparable to liver, the canonical site of haptoglobin production. This finding indicates that tumor-derived expression could contribute to elevated circulating proHp in at least a portion of patients. The authors used these observations to justify mechanistic studies assessing whether proHp has direct effects on tumor cell phenotypes.
To probe proHp function, the investigators generated HP knockout (HPKO) derivatives of the PSN1 pancreatic cancer cell line. In vitro, HPKO PSN1 cells exhibited reduced motility relative to wild-type cells. Supplementation of culture media with exogenous proHp partly rescued the motility deficit in HPKO PSN1 cells and increased motility when added to other pancreatic cancer cell lines. These results indicate that extracellular proHp can modulate migratory behavior in pancreatic cancer cells and that endogenous HP contributes to baseline motility in the PSN1 model.
In xenograft experiments, wild-type PSN1 cells formed rapidly growing tumors, whereas HPKO cells failed to produce the same aggressive growth in vivo. In vitro, wild-type PSN1 cells continued to proliferate beyond confluence, a phenotype that was lost in HPKO cells. The combined in vitro and in vivo data support a role for proHp in promoting tumor growth and the ability of cells to partially override contact-dependent growth inhibition.
The authors explored signaling mechanisms and focused on the Hippo–YAP axis. At high cell density, wild-type PSN1 cells maintained expression of YAP-related target genes and retained nuclear localization of YAP protein, despite activation of upstream Hippo signaling that typically excludes YAP from the nucleus. By contrast, HPKO cells showed reduced nuclear YAP and lower expression of YAP target genes at high density. The data are presented as evidence that proHp supports a noncanonical mechanism to sustain YAP activity when cells experience contact inhibition cues.
To test whether the proHp-dependent phenotypes are mediated through YAP, the investigators performed complementary gain- and loss-of-function interventions. Reintroduction or overexpression of YAP in HPKO cells restored high-density proliferation and cell motility, indicating that YAP is sufficient to rescue the defects caused by HP loss. Conversely, pharmacologic inhibition of the YAP–TEAD interaction selectively reduced high-density proliferation of wild-type cells but had no significant additional effect on HPKO cells. Together, these experiments support a model in which proHp enables pancreatic cancer cells to sustain YAP activity and thereby promotes proliferation and motility under conditions that normally restrict growth.
This preprint reports that prohaptoglobin can act as a tumor-promoting factor in pancreatic cancer models by maintaining YAP activity and allowing cells to partially overcome contact-dependent growth inhibition. Key observations include elevated serum proHp in patients, tumor cell HP expression in a subset of tumors and lines, reduced motility and loss of high-density proliferation with HP knockout, rescue of those phenotypes by exogenous proHp or restored YAP, and sensitivity of wild-type high-density proliferation to a YAP–TEAD inhibitor.
The authors conclude that proHp promotes pancreatic cancer progression in a context-dependent fashion through noncanonical support of YAP signaling. Because this report is a preprint, its findings should be interpreted as preliminary until peer review and independent validation are completed. Specific numeric data, full experimental protocols, and supplementary figures are provided in the source preprint but are not duplicated here.