Noncanonical role of singleminded-2s in mitochondrial respiratory chain formation in breast cancer.

Dysregulation of cellular metabolism is a hallmark of breast cancer progression and is associated with metastasis and therapeutic resistance. Here, we show that the breast tumor suppressor gene SIM2 promotes mitochondrial oxidative phosphorylation (OXPHOS) using breast cancer cell line models. Mechanistically, we found that SIM2s functions not as a transcription factor but localizes to mitochondria and directly interacts with the mitochondrial respiratory chain (MRC) to facilitate functional supercomplex (SC) formation. Loss of SIM2s expression disrupts SC formation through destabilization of MRC Complex III, leading to inhibition of electron transport, although Complex I (CI) activity is retained. A metabolomic analysis showed that knockout of SIM2s leads to a compensatory increase in ATP production through glycolysis and accelerated glutamine-driven TCA cycle production of NADH, creating a favorable environment for high cell proliferation. Our findings indicate that SIM2s is a novel stabilizing factor required for SC assembly, providing insight into the impact of the MRC on metabolic adaptation and breast cancer progression.

Rational Modulation of pH-Triggered Macromolecular Poration by Peptide Acylation and Dimerization.

The synthetically evolved pH-dependent delivery (pHD) peptides are a unique family that bind to membranes, fold into α-helices, and form macromolecule-sized pores at low concentration at pH < 6. These peptides have potential applications in drug delivery and tumor targeting. Here, we show how pHD peptide activity can be modulated without changing the amino acid sequence. We increased the hydrophobicity of a representative peptide, pHD108 (GIGEVLHELAEGLPELQEWIHAAQQLGC-amide), by coupling hydrophobic acyl groups of 6-16 carbons and by forming dimers. Unlike the parent peptide, almost all variants showed activity at pH 7. This was due to strong partitioning into phosphatidylcholine vesicle bilayers and induced helix formation. The dimer maintained some pH sensitivity while being the most active peptide studied in this work, with macromolecular poration occurring at 1:2000 peptide:lipid at pH 5. These results confirm that membrane binding, rather than pH, is the determining factor in activity, while also showing that acylation and dimerization are viable methods to modulate pHD108 activity. We propose a possible toroidal pore architecture with peptides in a parallel or mixed parallel/antiparallel orientation without strong electrostatic interactions between peptides in the pore as evidenced by a lack of dependence of activity on either pH or salt concentration.