Annexin A1 is a polarity cue that directs mitotic spindle orientation during mammalian epithelial morphogenesis

Abstract

Oriented cell divisions are critical for the formation and maintenance of structured epithelia. Proper mitotic spindle orientation relies on polarised anchoring of force generators to the cell cortex by the evolutionarily conserved protein complex formed by the Gαi subunit of heterotrimeric G proteins, the Leucine-Glycine-Asparagine repeat protein (LGN) and the nuclear mitotic apparatus protein. However, the polarity cues that control cortical patterning of this ternary complex remain largely unknown in mammalian epithelia. Here we identify the membrane-associated protein Annexin A1 (ANXA1) as an interactor of LGN in mammary epithelial cells. Annexin A1 acts independently of Gαi to instruct the accumulation of LGN and nuclear mitotic apparatus protein at the lateral cortex to ensure cortical anchoring of Dynein-Dynactin and astral microtubules and thereby planar alignment of the mitotic spindle. Loss of Annexin A1 randomises mitotic spindle orientation, which in turn disrupts epithelial architecture and luminogenesis in three-dimensional cultures of primary mammary epithelial cells. Our findings establish Annexin A1 as an upstream cortical cue that regulates LGN to direct planar cell divisions during mammalian epithelial morphogenesis.

Annexin A1, A2, A5, and A6 involvement in human pathologies

“…AnxA1 has recently been shown to be necessary for the correct orientation of the mitotic spindle in polarized epithelia, where it interacts directly or indirectly with LGN protein; a component of the mitotic apparatus. In mouse mammary cells knockdown of AnxA1 led to disorganized epithelial acini and led to random mitotic spindle apparatus orientation and loss of planar epithelial cell division 137 . AnxA2 has also been reported to participate in the early phase of cytokinesis, directing spindle‐equatorial plasma membrane communication essential for proper formation of the cortical cleavage furrow through association with cortical actin 138 .…”

“…AnxA2 is a tPA and plasminogen co‐receptor on endothelial surfaces and loss‐of‐function through reduced expression or chemical modification of its amino terminus through oxidative stress could mean that the vasculature was prone to fibrosis. A number of recent reviews have now considered annexin A1 and A2 role's in human biology and pathology 136,137 . AnxA5 has a well‐established anticoagulant activity, avidly binding to phosphatidyl serine exposed on cell surfaces and acting as a barrier to procoagulants.…”

Crosstalk between the plasma membrane and cell-cell adhesion maintains epithelial identity for correct polarised cell divisions

“…During mitosis, the Gαi-LGN-NuMA complex localises at the cell cortex, which facilitates the interaction of NuMA on astral microtubules and with the microtubule-associated minus-end motor Dynein, generating pulling forces on astral microtubules that ensure correct positioning of the mitotic spindle [3][4][5][6] . Cumulative evidence shows that the crosstalk between astral microtubules and cortical F-actin is a key mechanism for balancing the cortical forces that ensure correct mitotic spindle and chromosome dynamics, as well as mitosis progression [7][8][9][10] . In mammalian epithelia, polarity proteins including E-cadherin, Afadin, ABL1, SAPCD2 and Annexin A1 (ANXA1) have been shown to act as molecular landmarks instructing the polarised patterning of LGN and NuMA at the cell cortex to regulate the balance between planar and perpendicular mitotic spindle orientation 4,9,[11][12][13] .…”

“…Cumulative evidence shows that the crosstalk between astral microtubules and cortical F-actin is a key mechanism for balancing the cortical forces that ensure correct mitotic spindle and chromosome dynamics, as well as mitosis progression [7][8][9][10] . In mammalian epithelia, polarity proteins including E-cadherin, Afadin, ABL1, SAPCD2 and Annexin A1 (ANXA1) have been shown to act as molecular landmarks instructing the polarised patterning of LGN and NuMA at the cell cortex to regulate the balance between planar and perpendicular mitotic spindle orientation 4,9,[11][12][13] . Yet, the mechanisms coordinating the interplay between polarity cues, the cell cortex and the mitotic machinery in mammalian epithelial cells remain largely unknown.…”

“…Consequently, cells fail to correctly align the mitotic spindle and chromosomes, leading to delayed mitosis progression and cytokinesis defects. In this experimental context, we investigated the function of the membrane associated protein S100A11 (S100 Ca 2+ -binding protein A11), which we identified recently in a proteomic screening of mitotic mammary epithelial cells 9 . We demonstrate that S100A11 is required for proper plasma membrane remodelling to ensure faithful segregation of chromosomes and generation of equal-sized daughter cells.…”