Differential localizations of protein phosphatase 1 isoforms determine their physiological function in the heart

PP1 catalytic isoforms are differentially expressed and regulated in human prostate cancer

The Ser/Thr-protein phosphatase PP1 (PP1) is a positive regulator of the androgen receptor (AR), which suggests major roles for PP1 in prostate carcinogenesis. However, studies dedicated to the characterization of PP1 in PCa are currently scarce. Here we analyzed the expression and localization of the PP1 catalytic (PP1c) isoforms in formalin-fixed, paraffin-embedded prostate tissue samples, as well as in PCa cell lines. We also analyzed well-characterized PCa cohorts to determine their transcript levels, identify genetic alterations, and assess promoter methylation of PP1c-coding genes. We found that PP-1A was upregulated and relocalized towards the nucleus in PCa and that PPP1CA was frequently amplified in PCa, particularly in advanced stages. PP-1B was downregulated in PCa but upregulated in a subset of tumors with AR amplification. PP-1G transcript levels were found to be associated with Gleason score. PP1c-coding genes were rarely mutated in PCa and were not prone to regulation by promoter methylation. Protein phosphorylation, on the other hand, might be an important regulatory mechanism of PP1c isoforms' activity. Altogether, our results suggest differential expression, localization, and regulation of PP1c isoforms in PCa and support the need for investigating isoform-specific roles in prostate carcinogenesis in future studies.

Complex functionality of protein phosphatase 1 isoforms in the heart

Protein phosphatase 1(PP1) is a key regulator of cardiac function through dephosphorylating serine/threonine residues within target proteins to oppose the function of protein kinases. Studies from failing hearts of animal models and human patients have demonstrated significant increase of PP1 activity in myocardium, while elevated PP1 activity in transgenic mice leads to cardiac dysfunction, suggesting that PP1 might be a therapeutic target to ameliorate cardiac dysfunction in failing hearts. In fact, cardiac overexpression of inhibitor 1, the endogenous inhibitor of PP1, increases cardiac contractility and suppresses heart failure progression. However, this notion of PP1 inhibition for heart failure treatment has been challenged by recent studies on the isoform-specific roles of PP1 in the heart. PP1 is a holoenzyme composed of catalytic subunits (PP1α, PP1β, or PP1γ) and regulatory proteins that target them to distinct subcellular locations for functional specificity. This review will summarize how PP1 regulates phosphorylation of some of the key cardiac proteins involved in Ca²⁺ handling and cardiac contraction, and the potential role of PP1 isoforms in controlling cardiac physiology and pathophysiology.

A Chinese family with Noonan syndrome caused by a heterozygous variant in LZTR1: a case report and literature review

BACKGROUND

Noonan syndrome is an inherited disease involving multiple systems. More than 15 related genes have been discovered, among which LZTR1 was discovered recently. However, the pathogenesis and inheritance pattern of LZTR1 in Noonan syndrome have not yet been elucidated.

CASE PRESENTATION

We herein describe a family with LZTR1-related Noonan syndrome. In our study, the proband, sister, mother, maternal aunt and grandmother and female cousin showed the typical or atypical features of Noonan syndrome. Only 3 patients underwent the whole-exome sequencing analysis and results showed that the proband as well as her sister inherited the same heterozygous LZTR1 variant (c.1149 + 1G > T) from their affected mother. Moreover, the proband accompanied by growth hormone deficiency without other associated variants.

CONCLUSION

In a Chinese family with Noonan syndrome, we find that the c.1149 + 1G > T variant in LZTR1 gene shows a different autosomal dominant inheritance from previous reports, which changes our understanding of its inheritance and improves our understanding of Noonan syndrome.