The active form of the metabolic sensor AMP-activated protein kinase α (AMPKα) directly binds the mitotic apparatus and travels from centrosomes to the spindle midzone during mitosis and cytokinesis

Abstract

(2009) The active form of the metabolic sensor AMP-activated protein kinase α (AMPKα) directly binds the mitotic apparatus and travels from centrosomes to the spindle midzone during mitosis and cytokinesis, Cell Cycle, 8:15, 2385Cycle, 8:15, -2398 The metabolic rheostat AMP-activated protein kinase (AMPK) is unexpectedly required for proper cell division and faithful chromosomal segregation during mitosis. Although it is conceptually attractive to assume that AMPK-interpreted microenvironmental bioenergetics may strictly engage cell's energy status, cell grow, and cell division to avoid that energy stresses trigger cell death, the ultimate framework of AMPK activity towards chromosomal and cytoskeletal mitotic regulation is a question that remains unanswered. We herein reveal that the active form of the α-catalytic AMPK subunit (P-AMPKα Thr172 )-but not its total form (AMPKα)-transiently associates with several mitotic structures including centrosomes, spindle poles, the central spindle midzone and the midbody throughout all of the mitotic stages and cytokinesis in human cancer-derived epithelial cells. At prophase, P-AMPKα Thr172 associates with the two asters of microtubules that begin to nucleate from mature centrosomes. The overlapping localization of P-AMPKα Thr172 with the mitotic centrosomal Aurora-A kinase is also apparent on the microtubules near the spindle poles in metaphase and in early anaphase. This Aurora A-like centrosomal localization of P-AMPKα Thr172 cannot be detected following chromatid separation following anaphase-telophase transition. Rather, toward the end of anaphase and in telophase P-AMPKα Thr172 reactivity exhibited a similar but not identical localization to that occupied by the bona fide chromosomal passenger proteins INCENCP and Aurora-B. This localization of P-AMPKα Thr172 at the central spindle and midbody persisted during the furrowing process and, at the completion of telophase, staining of P-AMPKα Thr172 as doublet was apparent on either side of the midbody within the intercellular cytokinetic bridge. An identical mitotic geography of P-AMPKα Thr172 was observed in cancer cells lacking the AMPK kinase LKB1, in non-cancerous human epithelial cells, and in mouse fibroblasts. The active form of AMPKα bound to the mitotic apparatus may physically tether the bioenergetic state of a cell to the four-dimensional regulation of the chromosomal and cytoskeletal mitotic events, thus suggesting a putative cytokinetic suppressor function. In this newly discovered scenario, we suggest a primordial mitotic role for the α catalytic AMPK subunit in the eukaryotic evolutionary process as it may ensure, at the cell level, an exquisite coordination between sensing of energy resources and the fundamental biological process of genome division.

AMPK: Evidence for an energy-sensing cytokinetic tumor suppressor

“…18 This finding not only reveals that a non-metabolic function of AMPKα at centrosomes may be to sense and respond to structural or functional inactivation of the mitotic spindle but further supports the idea that both the cycling activation of AMPK at each mitotic onset and the pre-activated state of AMPKα during all the phases of a perturbed mitosis allows a mechanism readyto-act in response to bioenergetic stress and/or mitotic spindle impairment in the next G 1 phase of the cell cycle. such as the centrosomal Aurora A kinase and the chromosomal passenger proteins (CPPs) Aurora B and INCENP: 15,16 -Loss or depletion of these mitotic kinases produces phenocopies of the mitotic defects observed in cells lacking AMPK, including defects in chromosome segregation and failures in cytokinesis.…”

“…15,16 PP-AMPKα Thr172 , in an autonomous manner from AMPK regulatory subunits β and γ, physically associates with the mitotic apparatus to exhibit both centrosomal (i.e., Aurora A-like) and spindle midzone (i.e., CPP-like) localizations during mitosis and cytokinesis. 18 PP-AMPKα Thr172 localises at the poles of the mitotic spindle, adjacent to centrosomal Aurora A kinase in early mitosis, where it persists until late anaphase/telophase. In late mitosis, P-AMPKα Thr172 localises adjacent to the chromosomal passenger proteins Aurora B and INCENP at the central spindle midzone, and remains associated with the midbody in cytokinesis.…”

Raptor, a positive regulatory subunit of mTOR complex 1, is a novel phosphoprotein of the rDNA transcription machinery in nucleoli and chromosomal nucleolus organizer regions (NORs)

“…13 In this regard, we have previously reported that the active form of AMPK directly binds the mitotic apparatus and travels from centrosomes to the spindle midzone during mitosis. [32][33][34] Recently, we have established that polo-like kinase 1 (PLK1) is a novel regulator of AMPK activation at the mitotic apparatus. 35 These findings, altogether, may suggest the existence of a functional link connecting PLK1, AMPK and P-Raptor Ser722 during mitosis.…”

Mitotic figure counts are significantly overestimated in resection specimens of invasive breast carcinomas

“…However, in the absence of sustained energy supply, the gradually declining energy reserves will eventually arrest the cell cycle at the G2/M checkpoint; recent studies have shown that the mitotic machinery involves a metabolic sensor, the AMP-activated protein kinase, 20 which binds to various structures of the mitotic apparatus, including centrosomes, spindle poles and the spindle midzone. 21 This mechanism is understood as an energy gauge that assures that the cell disposes of sufficient energy to complete faithful chromosome separation and thus exerts an important cytokinetic suppressor function. 22 It is hence conceivable that mitotic activity continues in resection specimen up to the G2/M checkpoint, and that in the absence of sufficient energy reserves, tumor cells arrest in metaphase, where they are easily identified and counted by the diagnosing pathologist.…”