Serine palmitoyltransferase (SPT) predominantly incorporates
serine and fatty acyl-CoAs into diverse
sphingolipids (SLs) that serve as structural components of membranes and signaling molecules within or amongst cells. However, SPT also uses
alanine as a substrate in the contexts of low
serine availability,
alanine accumulation, or disease-causing mutations in
hereditary sensory neuropathy type I, resulting in the synthesis and accumulation of 1-deoxysphingolipids (deoxySLs). These species promote cytotoxicity in neurons and impact diverse cellular phenotypes, including suppression of anchorage-independent
cancer cell growth. While altered
serine and
alanine levels can promote 1-deoxySL synthesis, they impact numerous other metabolic pathways important for
cancer cells. Here, we combined
isotope tracing, quantitative metabolomics, and functional studies to better understand the mechanistic drivers of 1-deoxySL toxicity in
cancer cells. We determined that both
alanine treatment and SPTLC1C133W expression induce 1-deoxy(dihydro)ceramide synthesis and accumulation but fail to broadly impact intermediary metabolism, abundances of other
lipids, or growth of adherent cells. However, we found that spheroid culture and soft
agar colony formation were compromised when endogenous 1-deoxySL synthesis was induced via SPTLC1C133W expression. Consistent with these impacts on anchorage-independent cell growth, we observed that 1-deoxySL synthesis reduced plasma membrane endocytosis. These results highlight a potential role for SPT promiscuity in linking altered
amino acid metabolism to plasma membrane endocytosis.