During mitosis, CDK1 phosphorylates LBR (lamin B receptor) on N-terminal serine residues S71 and S86. S71 is the major CDK1 phosphorylation site in LBR (Tseng and Chen 2011).

Phosphorylation of LBR (lamin B receptor) at serine residue S71 drives binding of LBR to KPNB1 (importin beta) (Lu et al. 2010). This prevents premature association of nascent nuclear membranes with chromatin in anaphase (Tseng and Chen 2011). Dephosphorylation of this site is suggested to promote NE reassembly (Tseng and Chen 2011).

MECP2 and lamin B receptor (LBR) associate at the inner side of the nuclear envelope. The interaction involves the linker region of MECP2 and appears to happen in heterochromatin regions at the nuclear periphery (Guarda et al. 2009).

4,4-dimethylcholesta-8(9),14,24-trien-3beta-ol and NADPH + H+ react to form 4,4-dimethylcholesta-8(9),24-dien-3beta-ol and NADP+, catalyzed by LBR in the nuclear envelope. LBR protein spans the inner nuclear envelope, has an aminoterminal region with properties of a laminin receptor and a carboxyterminal domain with sequence similarity to sterol delta14-reductases (Holmer et al. 1998). Studies of material from an individual with HEM/Greenberg skeletal dysplasia indicate that LBR catalyzes the sterol delta14-reductase step of cholesterol biosynthesis in vivo. DNA sequencing revealed homozygosity for a mutant LBR allele encoding a truncated protein in the affected individual, and cells from the individual accumulated cholesta-8,14-dien-3beta-ol in culture. Transfection of wild-type LBR into the cultured cells reversed the accumulation of cholesta-8,14-dien-3beta-ol (Waterham et al. 2003). This observation is surprising because a second gene, TM7SF2, encodes an efficient sterol delta14-reductase that is localized to the endoplasmic reticulum whose expression is up-regulated in response to sterol depletion (Bennati et al. 2006). The physiological roles of LBR and TM7SF2 in vivo remain to be determined.

4,4-dimethylcholesta-8(9),14,24-trien-3beta-ol and NADPH + H+ react to form 4,4-dimethylcholesta-8(9),24-dien-3beta-ol and NADP+, catalyzed by TM7SF2 in the endoplasmic reticulum. TM7SF2 protein has sterol delta14-reductase activity in vitro, and expression of the gene is induced by sterol starvation in human cells, as expected for a gene involved in sterol biosynthesis (Bennati et al. 2006). However, molecular studies of material from an individual with HEM/Greenberg skeletal dysplasia indicate that LBR, a protein that spans the inner nuclear membrane and has both laminin receptor and sterol delta14-reductase activities, is required for normal sterol 14delta-reductase activity in human cells. It remains to be determined whether both LBR and TM7SF2 catalyze this reaction in vivo, and whether the role of TM7SF2 is essential (Waterham et al. 2003).

Activated GTP-bound CDC42 binds to kinectin (KTN1) at the endoplasmic reticulum membrane (Hotta et al. 1996).

Active CDC42 also binds the following candidate effectors at the endoplasmic reticulum membrane identified in the screen by Bagci et al. 2020:
LBR (Bagci et al. 2020)
YKT6 (Bagci et al. 2020)

Based on the high throughput screen conducted by Bagci et al. 2020, constitutively active RHOC binds to the following candidate effectors, known to reside at the endoplasmic reticulum membrane:
LBR (Bagci et al. 2020)
LMAN1 (Bagci et al. 2020)
MACO1 (Bagci et al. 2020)
PGRMC2 (Bagci et al. 2020)
STX5 (Bagci et al. 2020)
VAPB (Bagci et al. 2020)

Transcription of the MECP2 gene is known to be regulated by methylation of the promoter and the first intron, but the responsible methyltransferases are not known (Nagarajan et al. 2008, Franklin et al. 2010, Liyanage et al. 2013).

Translation of MECP2 mRNA is negatively regulated by the microRNA miR-132. Transcription of miR-132 is regulated by BDNF signaling, through an unknown mechanism (Klein et al. 2007, Su et al. 2015).

Binding of MECP2 to other proteins and to DNA is regulated by posttranslational modifications, of which phosphorylation has been best studied. Calcium dependent protein kinases, PKA and CaMK IV, activated by neuronal membrane depolarization, phosphorylate MECP2 at threonine residue T308 (corresponding to T320 in the longer MECP2 splicing isoform, MECP2_e1). Phosphorylation at T308 correlates with neuronal activity and inhibits binding of MECP2 to the nuclear receptor co-repressor complex (NCoR/SMRT) (Ebert et al. 2013). In resting neurons, MECP2 is phosphorylated at serine residue S80, which results in a decreased association of MECP2 with chromatin. Nuclear serine/threonine protein kinase HIPK2 phosphorylates MECP2 on serine residue S80 (Bracaglia et al. 2009). In activity-induced neurons, upon neuronal membrane depolarization, MECP2 S80 becomes dephosphorylated, and MECP2 acquires phosphorylation on serine S423 (corresponding to mouse Mecp2 serine S421). CaMK IV is one of the kinases that can phosphorylate MECP2 on S423. Phosphorylation of MECP2 at S423 increases MECP2 binding to chromatin (Zhou et al. 2006, Tao et al. 2009, Qiu et al. 2012). AURKB phosphorylates MECP2 at serine residue S423 in dividing adult neuronal progenitor cells (Li et al. 2014).

Besides binding to the NCoR/SMRT co-repressor complex (Lyst et al. 2013, Ebert et al. 2013), MECP2 binds the SIN3A co-repressor complex. This interaction involves the transcriptional repressor domain of MECP2 and the amino terminal part of the HDAC interaction domain (HID) of SIN3A. HDAC1 and HDAC2 are part of the SIN3A co-repressor complex that co-immunoprecipitates with MECP2 (Nan et al. 1998). While binding of MECP2 to SIN3A at target genes is associated with transcriptional repression, binding to CREB1 at target genes is associated with transcriptional activation (Chahrour et al. 2008, Chen et al. 2013). Function of MECP2 can be affected by binding to FOXG1, another gene mutated in Rett syndrome besides MECP2 and CDKL5 (Dastidar et al. 2012), and HTT (Huntingtin) (McFarland et al. 2013). The subnuclear localization of MECP2 may be affected by binding to the Lamin B receptor (LBR) (Guarda et al. 2009).