Sphingosine: A Modulator of Human Translesion DNA Polymerase Activity [DNA and Chromosomes]

June 13th, 2014 by Kamath-Loeb, A. S., Balakrishna, S., Whittington, D., Shen, J.-C., Emond, M. J., Okabe, T., Masutani, C., Hanaoka, F., Nishimura, S., Loeb, L. A.

Translesion (TLS) DNA polymerases are specialized, error-prone enzymes that synthesize DNA across bulky, replication-stalling DNA adducts. In so doing, they facilitate the progression of DNA synthesis and promote cell proliferation. In order to potentiate the effect of cancer chemotherapeutic regimens, we sought to identify inhibitors of TLS DNA polymerases. We screened five libraries of ~3000 small molecules, including one comprising ~600 nucleoside analogs, for their effect on primer extension activity of DNA Polymerase η (Pol η). We serendipitously identified sphingosine, a lipid-signaling molecule that robustly stimulates the activity of Pol η by ~100-fold at low micromolar concentrations, but inhibits it at higher concentrations. This effect is specific to the Y-family DNA Polymerases, Pols -η, -κ, and -ι. The addition of a single phosphate group on sphingosine completely abrogates this effect. Likewise, the inclusion of other sphingolipids, including ceramide and sphingomyelin to extension reactions does not elicit this response. Sphingosine increases the rate of correct and incorrect nucleotide incorporation, while having no effect on polymerase processivity. Endogenous Pol η activity is modulated similarly as the recombinant enzyme. Importantly, sphingosine-treated cells exhibit increased lesion bypass activity, and sphingosine tethered to membrane lipids mimics the effects of free sphingosine. Our studies have uncovered sphingosine as a modulator of TLS DNA polymerase activity; this property of sphingosine may be associated with its known role as a signaling molecule in regulating cell proliferation in response to cellular stress.