Proteoglycans are molecules that mediate interactions between cells and their environment. They play essential roles in inflammation, tissue remodeling, and cancer by modulating growth factor signaling and receptor binding.
Perlecan, a member of the proteoglycan family, is present in nearly all tissues. It regulates cell division, tumor cell invasiveness, and angiogenesis. In patients with aggressive melanoma, perlecan levels are elevated. In animal models, perlecan accumulates along the walls of newly formed vessels, forming a scaffold for their growth. It binds to fibroblast growth factor 2 (FGF2), acting as its receptor and promoting vascular formation. Studies in melanoma cells show that reducing perlecan decreases FGF2 activity. However, in fibrosarcoma cells, perlecan suppression paradoxically accelerates tumor formation – highlighting cell type–specific roles.
Perlecan expression begins early in embryogenesis, particularly in tissues forming the heart and large vessels. In adults, it is found in many organs, including lymphoid tissues, indicating its role in development and homeostasis.
Perlecan interacts not only with extracellular matrix components but also with signaling molecules such as TGF-β and IFN-γ. T lymphocytes primarily produce IFN-γ and exhibit antiviral, antiproliferative, and antitumor properties. It acts through the Stat protein family, which, upon activation, translocates to the nucleus and regulates gene expression.
IFN-γ Suppresses Perlecan and Inhibits Tumor Cell Growth
Researchers at Thomas Jefferson University (USA) found that IFN-γ reduces perlecan expression and inhibits tumor cell growth. This effect is reversible, does not require new protein synthesis, and is observed across various cell types. Perlecan gene suppression requires functional Stat1, which binds to specific regions in the gene’s promoter and inhibits transcription. Thus, IFN-γ may suppress tumor growth by removing a key angiogenic factor from the tumor microenvironment.
IFN-γ Inhibits Colorectal Cancer Cell Growth Independent of p21
In WiDr/HT29 colorectal carcinoma cells, which express high perlecan levels and respond to various growth factors, IFN-γ completely halted cell growth without inducing cell death. The effect was reversible. At a dose of 80 ng/mL, growth was nearly completely suppressed, with a half-maximal inhibitory concentration of approximately 50 ng/mL. Most cells accumulated in the G1 phase (50–73%), with reduced S and G2 populations.
To test whether p21 is required for this effect, the researchers used HCT116 colorectal carcinoma cells with a deleted p21 gene. Growth arrest and G1 accumulation occurred regardless of p21 status – indicating that IFN-γ halts colorectal cancer cell division independently of p21 and without inducing cell death.
IFN-γ Reversibly Suppresses Perlecan Gene Expression
Perlecan enhances tumor progression by amplifying angiogenic signals such as FGF2 and FGF7. In WiDr/HT29 colorectal cancer cells, IFN-γ reduced perlecan levels by 80% after 2 hours and by 90% after 4 hours. Perlecan mRNA levels also dropped sharply and remained low for up to 48 hours. Expression fully recovered after IFN-γ removal.
This effect was observed across cell lines derived from bone (Saos2), liver (HepG2), uterus (HeLa), colon (HCT116), and fibrous tissue (HT1080). It did not depend on p53, Rb, or p21.
IFN-γ Directly Inhibits Perlecan Gene Activity
Following IFN-γ exposure, perlecan mRNA and protein synthesis rapidly decreased – transcription fell within 2 hours and remained low for 4 hours. GAPDH transcription remained essentially unchanged, confirming the absence of cytotoxic effects.
Cycloheximide experiments revealed that IFN-γ acts via existing cellular proteins – new protein synthesis is not required for perlecan suppression.
Perlecan gene expression is highly responsive to cellular signals. Earlier studies in human melanoma cells showed that its mRNA levels shift within 10 minutes of nerve growth factor exposure. Therefore, perlecan levels reflect the balance of cytokines that either suppress or enhance its expression, modulating tumor cell growth and angiogenic potential.
Promoter deletion studies showed that IFN-γ suppressed perlecan transcription only when the whole 2.5 kb promoter region was present. This distal region contains GAS elements that Stat proteins bind to, enabling IFN-γ responsiveness.
Perlecan Suppression Requires Stat1
In Stat1-competent cells, IFN-γ inhibited cell growth and reduced perlecan protein levels by 55–60%. These effects were absent in Stat1-deficient cells. Thus, IFN-γ suppresses perlecan transcription only in the presence of functional Stat1.
Conclusion
Perlecan suppression may enhance the antitumor activity of IFN-γ, as this proteoglycan supports tumor growth and angiogenesis and is strategically located at the cell surface and basement membranes – key sites of lymphocyte–tumour interaction.
Therefore, IFN-γ may inhibit tumor growth both directly and indirectly by modulating the extracellular matrix through two mechanisms: reducing collagen synthesis and downregulating perlecan, a potent angiogenic factor. This positions IFN-γ as a foundation for developing novel cancer therapies targeting key regulators of tumor progression.
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Reference
Transcriptional Silencing of Perlecan Gene Expression by Interferon-γ
