Phosphorylation of MAK-V protein kinase in mammalian cells

Hormonally up-regulated neu-associated kinase: A novel target for breast cancer progression

Hormonally up-regulated neu-associated Kinase (Hunk) is a protein kinase that was originally identified in the murine mammary gland and has been shown to be highly expressed in Human Epidermal Growth Factor Receptor 2 positive (HER2+/ErbB2+) breast cancer cell lines as well as MMTV-neu derived mammary tumor cell lines. However, the physiological role of Hunk has been largely elusive since its identification. Though Hunk is predicted to be a Serine/Threonine (Ser/Thr) protein kinase with homology to the SNF1/AMPK family of protein kinases, there are no known Hunk substrates that have been identified to date. Recent work demonstrates a role for Hunk in HER2+/ErbB2+ breast cancer progression, including drug resistance to HER2/ErbB2 inhibitors, with Hunk potentially acting downstream of HER2/ErbB2 and the PI3K/Akt pathway. These studies have collectively shown that Hunk plays a vital role in promoting mammary tumorigenesis, as Hunk knockdown via shRNA in xenograft tumor models or crossing MMTV-neu or Pten-deficient genetically engineered mouse models into a Hunk knockout (Hunk-/-) background impairs mammary tumor growth in vivo. Because the majority of HER2+/ErbB2+ breast cancer patients acquire drug resistance to HER2/ErbB2 inhibitors, the characterization of novel drug targets like Hunk that have the potential to simultaneously suppress tumorigenesis and potentially enhance efficacy of current therapeutics is an important facet of drug development. Therefore, work aimed at uncovering specific regulatory functions for Hunk that could contribute to this protein kinase's role in both tumorigenesis and drug resistance will be informative. This review focuses on what is currently known about this under-studied protein kinase, and how targeting Hunk may prove to be a potential therapeutic target for the treatment of breast cancer.

Identification of Nedd4 E3 ubiquitin ligase as a binding partner and regulator of MAK-V protein kinase

MAK-V/Hunk is a scantily characterized AMPK-like protein kinase. Recent findings identified MAK-V as a pro-survival and anti-apoptotic protein and revealed its role in embryonic development as well as in tumorigenesis and metastasis. However molecular mechanisms of MAK-V action and regulation of its activity remain largely unknown. We identified Nedd4 as an interaction partner for MAK-V protein kinase. However, this HECT-type E3 ubiquitin ligase is not involved in the control of MAK-V degradation by the ubiquitin-proteasome system that regulates MAK-V abundance in cells. However, Nedd4 in an ubiquitin ligase-independent manner rescued developmental defects in Xenopus embryos induced by MAK-V overexpression, suggesting physiological relevance of interaction between MAK-V and Nedd4. This identifies Nedd4 as the first known regulator of MAK-V function.

Studying protein phosphorylation in low MW CSF fractions with capLC-ICPMS and nanoLC-CHIP-ITMS for identification of phosphoproteins

An initial study of protein phosphorylation in human cerebral spinal fluid (CSF) is described. CSF is an important body fluid for study of proteins and metabolites and may lead to the ultimate development of molecular markers to predict neurological diseases or their complications, such as in the case of hemorrhagic stroke. The use of capillary liquid chromatography coupled to inductively coupled plasma mass spectrometry (capLC-ICPMS) for screening using (31)P as the internal elemental tag atom at ultratrace levels, in combination with molecular mass spectrometry using Spectrum Mill and MASCOT database search engines for peptide identification, is a novel approach in its application to CSF relevant phosphopeptides and phosphorylated proteins. CapLC-ICPMS combined with nano liquid chromatography electrospray ionization, ion trap mass spectrometry (nanoLC-CHIP/ITMS), was utilized for initial experiments with CSF. Specific low-level screening for (31)P containing compounds is accomplished, and nanoLC-CHIP/ITMS provided the corresponding peptide information and subsequent protein identifications. The fractions containing (31)P from screening by the capLC-ICPMS were collected offline and analyzed separately with nanoLC-CHIP/ITMS. Synthetic phosphopeptides were used to test the method and to estimate lowest quantifiable limits for phosphorus. Tryptically digested beta-casein was then used to demonstrate the viability of the methodology for the complex CSF matrix from hemorrhagic stroke patients while also analyzing for native phosphopeptides in the CSF.