SIPA1 enhances SMAD2/3 expression to maintain stem cell features in breast cancer cells

Area of Science:

• Oncology
• Molecular Biology
• Cell Biology

Background:

• Signal-inhibiting protein 1 (SIPA1) is a GTPase activating protein known to negatively regulate Ras-related protein (Rap).
• SIPA1 has been implicated as a potential modulator of tumor metastasis and recurrence in various cancers.

Purpose of the Study:

• To investigate the role of SIPA1 in promoting breast cancer stemness and chemoresistance.
• To elucidate the molecular mechanisms underlying SIPA1-mediated effects, focusing on SMAD signaling pathways.

Main Methods:

• Assessed tumorsphere formation and CD44 expression to evaluate stemness features in breast cancer cells.
• Measured the expression of stemness-associated transcription factors and SMAD2/SMAD3 levels in vitro and in vivo.
• Utilized SIS3, a specific inhibitor of SMAD3 phosphorylation, to block signaling pathways.

Main Results:

• SIPA1 significantly enhanced stemness features, including tumorsphere formation and CD44 expression, in breast cancer cells.
• SIPA1 promoted the expression of four stemness-associated transcription factors by upregulating SMAD2 and SMAD3.
• SIPA1 decreased breast cancer cell sensitivity to chemotherapy, an effect reversed by SIS3 treatment, which also abolished stemness features.

Conclusions:

• SIPA1 promotes and sustains breast cancer cell stemness and chemoresistance by increasing SMAD2 and SMAD3 expression.
• Blocking SMAD3 phosphorylation with SIS3 can suppress cancer stemness and enhance chemotherapy sensitivity in SIPA1-high breast cancer cells.