Mammalian cellular apoptosis susceptibility (CAS) proteins are homologous to the yeast chromosome-segregation protein, CSE1 [1]. This family aligns the C-terminal halves (approximately). CAS is involved in both cellular apoptosis and proliferation [2,3]. Apoptosis is inhibited in CAS-depleted cells, while the expression of CAS correlates to the degree of cellular proliferation. Like CSE1, it is essential for the mitotic checkpoint in the cell cycle (CAS depletion blocks the cell in the G2 phase), and has been shown to be associated with the microtubule network and the mitotic spindle [3], as is the protein MEK, which is thought to regulate the intracellular localisation (predominantly nuclear vs. predominantly cytosolic) of CAS. In the nucleus, CAS acts as a nuclear transport factor in the importin pathway [4]. The importin pathway mediates the nuclear transport of several proteins that are necessary for mitosis and further progression. CAS is therefore thought to affect the cell cycle through its effect on the nuclear transport of these proteins [4]. Since apoptosis also requires the nuclear import of several proteins (such as P53 and transcription factors), it has been suggested that CAS also enables apoptosis by facilitating the nuclear import of at least a subset of these essential proteins [5].

1: Cloning and characterization of a cellular apoptosis susceptibility gene, the human homologue to the yeast chromosome segregation gene CSE1. Brinkmann U, Brinkmann E, Gallo M, Pastan I; Proc Natl Acad Sci U S A 1995;92:10427-10431. PMID:7479798

2: Role of CAS, a human homologue to the yeast chromosome segregation gene CSE1, in toxin and tumor necrosis factor mediated apoptosis. Brinkmann U, Brinkmann E, Gallo M, Scherf U, Pastan I; Biochemistry 1996;35:6891-6899. PMID:8639641

3: The human CAS protein which is homologous to the CSE1 yeast chromosome segregation gene product is associated with microtubules and mitotic spindle. Scherf U, Pastan I, Willingham MC, Brinkmann U; Proc Natl Acad Sci U S A 1996;93:2670-2674. PMID:8610099

4: Export of importin alpha from the nucleus is mediated by a specific nuclear transport factor. Kutay U, Bischoff FR, Kostka S, Kraft R, Gorlich D; Cell 1997;90:1061-1071. PMID:9323134

5: CAS, the human homologue of the yeast chromosome-segregation gene CSE1, in proliferation, apoptosis, and cancer. Brinkmann U; Am J Hum Genet 1998;62:509-513. PMID:9497270

6: The structure of the nuclear export receptor Cse1 in its cytosolic state reveals a closed conformation incompatible with cargo binding. Cook A, Fernandez E, Lindner D, Ebert J, Schlenstedt G, Conti E; Mol Cell 2005;18:355-367. PMID:15866177