Hutchinson-Gilford progeria syndrome (HGPS) is a rare autosomal dominant genetic disease that is caused by a silent mutation of the LMNA gene encoding lamins A and C (lamin A/C). The G608G mutation generates a more accessible splicing donor site than does WT and produces an alternatively spliced product of LMNA called progerin, which is also expressed in normal aged cells. In this study, we determined that progerin binds directly to lamin A/C and induces profound nuclear aberrations. Given this observation, we performed a random screening of a chemical library and identified 3 compounds (JH1, JH4, and JH13) that efficiently block progerin–lamin A/C binding. These 3 chemicals, particularly JH4, alleviated nuclear deformation and reversed senescence markers characteristic of HGPS cells, including growth arrest and senescence-associated β-gal (SA–β-gal) activity. We then used microarray-based analysis to demonstrate that JH4 is able to rescue defects of cell-cycle progression in both HGPS and aged cells. Furthermore, administration of JH4 to Lmna^G609G/G609G-mutant mice, which phenocopy human HGPS, resulted in a marked improvement of several progeria phenotypes and an extended lifespan. Together, these findings indicate that specific inhibitors with the ability to block pathological progerin–lamin A/C binding may represent a promising strategy for improving lifespan and health in both HGPS and normal aging.

So-mi Kang, Min-Ho Yoon & Bum-Joon Park*. BMB Reports 2018;51:327-37. https://doi.org/10.5483/BMBRep.2018.51.7.113

Leucine-rich repeat kinase 2 (LRRK2) is a gene in which a mutation causes Parkinson’s disease (PD), and p53 is a prototype tumor suppressor. In addition, activation of p53 in patient with PD has been reported by several studies. Because phosphorylation of p53 is critical for regulating its activity and LRRK2 is a kinase, we tested whether p53 is phosphorylated by LRRK2. LRRK2 phosphorylates threonine (Thr) at TXR sites in an in vitro kinase assay, and the T304 and T377 were identified as putative phosphorylated residues. An increase of phospho-Thr in the p53 TXR motif was confirmed in the cells overexpressing G2019S, and human induced pluripotent stem (iPS) cells of a G2019S carrier. Interactions between LRRK2 and p53 were confirmed by co-immunoprecipitation of lysates of differentiated SH-SY5Y cells. LRRK2 mediated p53 phosphorylation translocalizes p53 predominantly to nucleus and increases p21WAF1/CIP1 expression in SH-SY5Y cells based on reverse transcription-polymerase chain reaction and Western blot assay results. The luciferase assay using the p21WAF1/CIP1 promoter-reporter also confirmed that LRRK2 kinase activity increases p21 expression. Exogenous expression of G2019S and the phosphomimetic p53 T304/377D mutants increased expression of p21WAF1/CIP1 and cleaved PARP, and cytotoxicity in the same cells. We also observed increase of p21 expression in rat primary neuron cells after transient expression of p53 T304/377D mutants and the mid-brain lysates of the G2019S transgenic mice. p53 is a LRRK2 kinase substrate. Phosphorylation of p53 by LRRK2 induces p21WAF1/CIP1 expression and apoptosis in differentiated SH-SY5Y cells and rat primary neurons.

P53-mediated cellular senescence has been intensively investigated, because it is important for tumor suppressive function. In addition, p16/INK4A is well known to be critical for cellular senescence. However, detailed molecular mechanism or relevance between p53 and p16-mediated senescence has not been demonstrated yet. Here we show that p53 induces p16 through Lamin A/C stabilization via direct interaction. Stabilized Lamin A/C promotes degradation of BMI-1 and MEL-18 (Polycomb repressor complex 1, PRC1), which sequesters p16 promotor. Increased p53 can reduce BMI-1/MEL-18 and induce p16 expression via Lamin A/C. Elimination of Lamin A/C can abolish p53-induced p16 expression and BMI-1/MEL-18 reduction. As Lamin A/C expression is increased during cell differentiation, this mechanism seems to be very useful for selective induction of senescence in non-stem cells. Our results suggest that Lamin A/C-p53 network is important for p16/INK4A-mediated cellular senescence.

P53 is frequently mutated by genetic alternation or suppressed by various kinds of cellular signaling pathways in human cancers. Recently, we have revealed that p53 is suppressed and eliminated from cells by direct binding with oncogenic K-Ras-induced Snail. On the basis of the fact, we generated specific inhibitors against p53-Snail binding (GN25 and GN29). These chemicals can induce p53 expression and functions in K-Ras-mutated cells. However, it does not show cytotoxic effect on normal cells or K-Ras-wild-type cells. Moreover, GN25 can selectively activate wild-type p53 in p53^WT/MT cancer cells. But single allelic mt p53 containing cell line, Panc-1, does not respond to our chemical. In vivo xenograft test also supports the antitumor effect of GN25 in K-Ras-mutated cell lines. These results suggest that our compounds are strong candidate for anticancer drug against K-Ras-initiated human cancers including pancreatic and lung cancers.

Previous work has revealed that progerin-lamin A binding inhibitor (JH4) can ameliorate pathological features of Hutchinson-Gilford progeria syndrome (HGPS) such as nuclear deformation, growth suppression in patient’s cells, and very short life span in an in vivo mouse model. Despite its favorable effects, JH4 is rapidly eliminated in in vivo pharmacokinetic (PK) analysis. Thus, we improved its property through chemical modification and obtained an optimized drug candidate, Progerinin (SLC-D011). This chemical can extend the life span of Lmna ^G609G/G609G mouse for about 10 weeks and increase its body weight. Progerinin can also extend the life span of Lmna ^G609G/+ mouse for about 14 weeks via oral administration, whereas treatment with lonafarnib (farnesyl-transferase inhibitor) can only extend the life span of Lmna ^G609G/+ mouse for about two weeks. In addition, progerinin can induce histological and physiological improvement in Lmna ^G609G/+ mouse. These results indicate that progerinin is a strong drug candidate for HGPS.