Gorr 2018 MiP2018
Myoglobin (MB) in terrestrial mammals canonically functions as O2 transporter from cell surfaces to mitochondria when present at 250 - 750 μM concentrations in myocytes of striated muscles. Several years ago, however, we co-discovered MB of ´mice and men´ to be expressed in milk duct-lining secretory cells of healthy breasts and luminal-type breast cancer (herein: BrCa; see Fig. 1A-1C). Expression of MB in these carcinomas correlates with hormone receptor positivity (ERα), thus yielding a significantly better prognostic outcome (Fig. 1D) [1-4]. This non-canonical and low-level MB expression clearly is of clinical significance.
Increasing evidence obtained by others and us underscores the notion that MB in epithelial cancer cells, at its low-level abundance (i.e. nM - low μM), rather governs both turnover and deposition of long chain fatty acids (FAs) than acting as effective O2 supply vehicle. In support of published in vitro data, the selective presence of MB in the lipid-secreting luminal epithelia of the breast (Fig. 1A-1C) early on suggested that, in vivo, the protein might facilitate the trafficking and secretion of FAs into the lipid fraction of the milk. FA profiles, acquired in the meantime from in vivo (i.e. mouse milk, brown adipose tissue) and in vitro materials (i.e. MEFs, BrCa cells) with MB-proficient vs. MB-deficient background, consistently demonstrated the globin´s direct or indirect ability to impair the desaturation of long-chain FAs and to promote both full (β-oxidation) and limited oxidation of FAs in mitochondria and peroxisomes, respectively. In pursuing this further, we utilized MB wild type (MBwt) and Crispr/Cas-engineered MB knockout (MBko) clones of MCF7 BrCa cells that were incubated with the fluorigenic C16 FA palmitate derivative Bodipy-FL C16 and subjected to normoxic (Nx, air/72h) and hypoxic (Hx, 0.2% O2/72h) atmospheres. These analyses clearly revealed the existence of an O2-dependent trafficking of Bodipy-FL C16 between cytosolic and vesicular compartments by MB in MCF7 cells.
However, cancer cell MB also seems to affect tumor growth and virulence in ways independent from its actions on FA homeostasis. This relevant tumor control function (see Fig. 1D) might be exerted either by the globin itself or through its increasingly evidenced bi-directional feed-forward interplay with the established tumor suppressor p53. Because loss of p53 function is the most common cause of breast cancer related to a single gene, two PhD students (i.e. J. Armbruster, M.A. Aboouf) are currently examining MB´s role in breast tumor formation and progression through in vitro studies (breast cancer cell clones; Crispr/Cas9-engineered for MB or p53 knockout), and in vivo mouse models (i.e. crossing of: i) WapCre,Trp53flox animals with Mb-/- mice; ii) PyMT with Mb-/- mice) to obtain spontaneously forming breast tumors, with and without myoglobin, and in backgrounds ranging from p53 wild-type to p53 loss-of-function to p53 mono- or bi-allelic deficiency. With help of these models we are currently gathering data on the function of cancer-cell expressed MB - for all clinically relevant p53 backgrounds - with regard to the cellular or tumor tissue viability, proliferation, respiratory activity, fatty acid homeostasis and trafficking, dissemination as well as pharmacological or radiological treatability. This talk will provide an up-to-date overview on key findings of novel MB´s roles in a) FA homeostasis and b) p53-mediated tumor progression. In addition, the talk will highlight open questions and provide an outlook towards establishing MB as novel diagnostic and therapeutic marker in human or veterinary medicine.
Labels: MiParea: Genetic knockout;overexpression, mt-Medicine Pathology: Cancer
Organism: Human, Mouse Tissue;cell: Other cell lines
Armbruster J(1)*, Aboouf MA(1)*, Zhu H(2), Kristiansen G(3), Bicker A(4), Hankeln T(4), Gorr TA(1)#
- Univ Zurich, Inst Vet Physiol, Zurich, Switzerland
- Univ Kansas Med Center, Kansas City, MO, USA
- Univ-Hospital Bonn, Inst Pathol, Bonn
- Univ Mainz, Inst Org Mol Evolution, Mainz; Germany
*contributed equally to this work; #corresponding/presenting author: Gorr TA, [email protected]
Figure 1. MB expression in the breast. In lobular parenchyma of normal human breast (A): MB mildly expressed in luminal epithelial cells (inner layer, arrows), not in myoepithelial cells (outer layer, arrow-head). (B) Similar Mb localization in murine breast. (C) Well-differentiated human invasive ductal carcinoma with strong MB expression. (D) Kaplan Meier analysis of 872 primary breast cancer patients indicates that MB adds prognostic information to estrogen receptor (ER) status. Tumors positive for either ER or MB show intermediate course of cumulative patient survival relative to doubly positive or doubly negative entities. (E) Mb protein expression in three of four mice with spontaneous breast tumors (WapCre;Trp53flox models).
- Kristiansen G, Rose M, Geisler C, Fritzsche FR, Gerhardt J, Lüke C, Ladhoff AM, Knüchel R, Dietel M, Moch H, Varga Z, Theurillat JP, Gorr TA, Dahl E (2010) Endogenous myoglobin in human breast cancer is a hallmark of luminal cancer phenotype. Br J Can. 102:1736-45.
- Gorr TA, Wichmann D, Pilarsky C, Theurillat JP, Fabrizius A, Laufs T, Bauer T, Koslowski M, Horn S, Burmester T, Hankeln T, Kristiansen G (2011) Old proteins - new locations: myoglobin, haemoglobin, neuroglobin and cytoglobin in solid tumours and cancer cells. Acta Physiol 202:563-81.
- Kristiansen G, Hu J, Wichmann D, Stiehl DP, Rose M, Gerhardt J, Bohnert A, ten Haaf A, Moch H, Raleigh J, Varia MA, Subarsky P, Scandurra FM, Gnaiger E, Gleixner E, Bicker A, Gassmann M, Hankeln T, Dahl E, Gorr TA (2011) Endogenous myoglobin in breast cancer is hypoxia-inducible by alternative transcription and functions to impair mitochondrial activity: a role in tumor suppression? J Biol Chem 286:43417-28.
- Bicker A, Dietrich D, Gleixner E, Kristiansen G, Gorr TA, Hankeln T (2014) Extensive transcriptional complexity during hypoxia-regulated expression of the myoglobin gene in cancer. Hum Mol Genet 23:479-90.