Mapping the phosphorylation sites of Ulk1.

Ulk1 is a serine/threonine kinase that controls macroautophagy, an essential homeostatic recycling pathway that degrades bulk cytoplasmic material and directs the turnover of organelles such as peroxisomes and mitochondria. Further, macroautophagy is potently induced by signals that trigger metabolic stress, such as hypoxia and amino acid starvation, where its recycling functions provide macromolecules necessary to maintain catabolic metabolism and cell survival. Substrates for Ulk1 have not been identified, and little is known regarding post-translational control of Ulk1 kinase activity and function. To gain insights into the regulatory mechanisms of Ulk1, we developed a robust purification protocol for Ulk1 and demonstrated that Ulk1 is highly phosphorylated and requires autophosphorylation for stability. Importantly, high-resolution, tandem mass spectrometry identified multiple sites of phosphorylation on Ulk1, including several within domains known to regulate macroautophagy. Differential phosphorylation analyses also identified sites of phosphorylation in the C-terminal domain that depend upon or require Ulk1 autophosphorylation.

The relevance of sequence insertions in the Mcl-1 promoter in chronic lymphocytic leukemia and in normal cells.

We measured the frequency of insertions in the Mcl-1 promoter in chronic lymphocytic leukemia (CLL) and in normal individuals. Insertions were found in 37/54 (69%) of the CLL samples. However, insertions were not associated with prognostic markers and were also detected in 38/66 (58%) of normal controls and in normal cells isolated from CLL patients. Thus, Mcl-1 insertions are not acquired during leukemogenesis and are unlikely to play an important role in this disease.