20.500.12556/DiRROS-29359 Stefin B and cystatin C deficiency suppresses tumor growth and alters tumor microenvironment in a breast cancer model Background/Objectives: Cysteine cathepsins and their endogenous inhibitors have been shown to possess context-dependent functions in cancer progression, including the regulation of tumor metabolic pathways. Stefin B and cystatin C, intracellular and extracellular protease inhibitors, respectively, can modulate tumor biology through protease-dependent and protease-independent mechanisms. This study investigated their combined functions and potential roles as tumor promoters in breast cancer in a spontaneous breast cancer mouse model (PyMT mice). Methods: We generated PyMT transgenic mice lacking both stefin B and cystatin C (double-knockout, DKO) and compared their tumor growth kinetics, proliferation, apoptosis, and metastatic burden with those of wild-type control mice. Immunohistochemistry was performed to characterize tumor macrophage infiltration and polarization. Results: DKO mice demonstrated delayed tumor onset, significantly slower tumor growth, reduced proliferation, increased apoptosis, and fewer lung metastases compared to wild-type controls. Immunohistochemistry revealed enhanced macrophage infiltration of the tumors, accompanied by a pronounced shift toward antitumorigenic M1 (CD86+) polarization, while M2 (CD206+) populations remained unchanged, indicating an immunological reprogramming of the tumor microenvironment toward a pro-inflammatory, tumor-suppressive state. Conclusions: Our results demonstrated a potential function of stefin B and cystatin C as tumor promoters in breast cancer through complementary mechanisms. Simultaneous depletion of both inhibitors revealed synergistic effects and remodeled the immune microenvironment to favor tumor suppression. These results suggest previously unknown roles for stefin B and cystatin C in tumor development and progression, which encourage further investigation of the cancer metabolic mechanisms underlying tumor behavior and their dynamic interplay with the microenvironment. cystatin C stefin B tumor microenvironment cysteine cathepsins cancer metabolism protease inhibitors cistatin C stefin B mikrookolje tumorja cisteinski katepsini metabolizem raka true false true MDPI Švica Angleški jezik Slovenski jezik © 2026 by the authors. Neznano 2026-05-12 11:49:50 2026-05-12 11:49:51 2026-05-13 03:45:24 0000-00-00 00:00:00 2026 0 0 Nasl. z nasl. zaslona; Soavtorji: Janja Završnik, Miha Butinar, Georgy Mikhaylov, Boris Turk, Olga Vasiljeva; Opis vira z dne 11. 5. 2026; str. 1-19 iss. 4, [article no.] 360 Vol. 15 Feb. 2026 0000-00-00 Zaloznikova Objavljeno NiDoloceno 2026-01-10 2026-02-12 2026-02-17 577 2073-4409 10.3390/cells15040360 277698563 https://www.mdpi.com/2073-4409/15/4/360# 1 ee027f43-4de7-11f1-8a5a-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=43983 RAZ_Matjan-Stefin_Petra_2026.pdf RAZ_Matjan-Stefin_Petra_2026.pdf 1 4D905AD1EE4FE6445CD66AB952C76563 64394871a9b903e763e60196c3a2556b800eab11b5efa0ff2df5790804dd2417 35b0158a-4de8-11f1-8a5a-001a4af901a5 https://dirros.openscience.si/Dokument.php?lang=slv&id=43984 Institut Jožef Stefan 0 0 0