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STRAD pseudokinases regulate axogenesis and LKB1 stability.

Veleva-Rotse BO, Smart JL, Baas AF, Edmonds B, Zhao ZM, Brown A, Klug LR, Hansen K, Reilly G, Gardner AP, Subbiah K, Gaucher EA, Clevers H, Barnes AP - Neural Dev (2014)

Bottom Line: We find that STRADα is highly spliced and appears to be the primal STRAD paralog.We also reveal a reciprocal protein-stabilizing relationship in vivo between LKB1 and STRADα, whereby STRADα specifically maintains LKB1 protein levels via cytoplasmic compartmentalization.We demonstrate a novel role for STRADβ in axogenesis and also show for the first time in vivo that STRADα, but not STRADβ, is responsible for LKB1 protein stability.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pediatrics-Doernbecher, Children's Hospital, Portland, OR 97239, USA. barnesan@ohsu.edu.

ABSTRACT

Background: Neuronal polarization is an essential step of morphogenesis and connectivity in the developing brain. The serine/threonine kinase LKB1 is a key regulator of cell polarity, metabolism, tumorigenesis, and is required for axon formation. It is allosterically regulated by two related and evolutionarily conserved pseudokinases, STe20-Related ADapters (STRADs) α and β. The roles of STRADα and STRADβ in the developing nervous system are not fully defined, nor is it known whether they serve distinct functions.

Results: We find that STRADα is highly spliced and appears to be the primal STRAD paralog. We report that each STRAD is sufficient for axogenesis and promoting cell survival in the developing cortex. We also reveal a reciprocal protein-stabilizing relationship in vivo between LKB1 and STRADα, whereby STRADα specifically maintains LKB1 protein levels via cytoplasmic compartmentalization.

Conclusions: We demonstrate a novel role for STRADβ in axogenesis and also show for the first time in vivo that STRADα, but not STRADβ, is responsible for LKB1 protein stability.

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Related in: MedlinePlus

STRAD splice forms are expressed in a tissue-specific manner. (A) Schematic of mouse STRADα and STRADβ proteins indicating percent similarity between the two proteins. (B) Schematic of phylogenetic tree based on the STRAD gene from Bilaterians using Cnidaria as the outgroup with posterior probabilities indicating support for nodes (0–1, 1 being the strongest support) labeled on nodes of interest. The tree is based on MrBayes phylogenetic analysis (see Additional file 1: Figure S1). (C) Quantitative real-time-PCR of STRADα and STRADβ across developmental time. (D) Reverse transcriptase-PCR (RT-PCR) of STRADα indicates that multiple variants exist in distinct tissue types. In particular, the largest species (arrowhead) appears to be specific to brain, skeletal muscle and testes. (E) RT-PCR products from enriched cultures of the dominant CNS cell types. (STRADα-1 isoform – arrowhead; STRADα-4 isoform - asterisk). Cort neurons – cerebral cortex primary neurons; Interneurons – medial ganglionic eminence primary neurons, Astrocytes – primary post-natal day 1 astrocytes, Oligo – primary oligodendrocyte cultures. (F) RT-PCR of STRADα isoforms across developmental time in the cerebal cortex. CNS, central nervous system.
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Figure 1: STRAD splice forms are expressed in a tissue-specific manner. (A) Schematic of mouse STRADα and STRADβ proteins indicating percent similarity between the two proteins. (B) Schematic of phylogenetic tree based on the STRAD gene from Bilaterians using Cnidaria as the outgroup with posterior probabilities indicating support for nodes (0–1, 1 being the strongest support) labeled on nodes of interest. The tree is based on MrBayes phylogenetic analysis (see Additional file 1: Figure S1). (C) Quantitative real-time-PCR of STRADα and STRADβ across developmental time. (D) Reverse transcriptase-PCR (RT-PCR) of STRADα indicates that multiple variants exist in distinct tissue types. In particular, the largest species (arrowhead) appears to be specific to brain, skeletal muscle and testes. (E) RT-PCR products from enriched cultures of the dominant CNS cell types. (STRADα-1 isoform – arrowhead; STRADα-4 isoform - asterisk). Cort neurons – cerebral cortex primary neurons; Interneurons – medial ganglionic eminence primary neurons, Astrocytes – primary post-natal day 1 astrocytes, Oligo – primary oligodendrocyte cultures. (F) RT-PCR of STRADα isoforms across developmental time in the cerebal cortex. CNS, central nervous system.

Mentions: The vast networks of neural projections in the brain are essential for appropriate connectivity, but how these axons are specified during neuronal differentiation remains unclear. The regulatory mechanisms coordinating axon formation are only beginning to emerge despite the identification of key signaling molecules [1-3]. The protein kinase Liver Kinase B1 (LKB1) is a requisite component of the transduction machinery controlling axon specification both in vitro and in vivo [4,5]. LKB1 catalytic activity is allosterically regulated by the related pseudokinases, STRAD (STe20 Related ADapter)-alpha and STRAD-beta (STRADα and STRADβ) (Figure 1A, [6,7]). While little is known about STRADβ function, homozygous deletion within the human LYK5 (STRADα) locus (see Additional file 1: Figure S3A) results in a syndromic condition known as polyhydramnios, megalencephaly, and symptomatic epilepsy (PMSE) [8]. These patients have craniofacial dysmorphology, cognitive deficits, and intractable infantile-onset epilepsy. Given the clear impact on human health and brain development, further insights into STRAD pseudokinases are needed to clarify their contributions to nervous system development and disease.


STRAD pseudokinases regulate axogenesis and LKB1 stability.

Veleva-Rotse BO, Smart JL, Baas AF, Edmonds B, Zhao ZM, Brown A, Klug LR, Hansen K, Reilly G, Gardner AP, Subbiah K, Gaucher EA, Clevers H, Barnes AP - Neural Dev (2014)

STRAD splice forms are expressed in a tissue-specific manner. (A) Schematic of mouse STRADα and STRADβ proteins indicating percent similarity between the two proteins. (B) Schematic of phylogenetic tree based on the STRAD gene from Bilaterians using Cnidaria as the outgroup with posterior probabilities indicating support for nodes (0–1, 1 being the strongest support) labeled on nodes of interest. The tree is based on MrBayes phylogenetic analysis (see Additional file 1: Figure S1). (C) Quantitative real-time-PCR of STRADα and STRADβ across developmental time. (D) Reverse transcriptase-PCR (RT-PCR) of STRADα indicates that multiple variants exist in distinct tissue types. In particular, the largest species (arrowhead) appears to be specific to brain, skeletal muscle and testes. (E) RT-PCR products from enriched cultures of the dominant CNS cell types. (STRADα-1 isoform – arrowhead; STRADα-4 isoform - asterisk). Cort neurons – cerebral cortex primary neurons; Interneurons – medial ganglionic eminence primary neurons, Astrocytes – primary post-natal day 1 astrocytes, Oligo – primary oligodendrocyte cultures. (F) RT-PCR of STRADα isoforms across developmental time in the cerebal cortex. CNS, central nervous system.
© Copyright Policy - open-access
Related In: Results  -  Collection

License 1 - License 2
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Figure 1: STRAD splice forms are expressed in a tissue-specific manner. (A) Schematic of mouse STRADα and STRADβ proteins indicating percent similarity between the two proteins. (B) Schematic of phylogenetic tree based on the STRAD gene from Bilaterians using Cnidaria as the outgroup with posterior probabilities indicating support for nodes (0–1, 1 being the strongest support) labeled on nodes of interest. The tree is based on MrBayes phylogenetic analysis (see Additional file 1: Figure S1). (C) Quantitative real-time-PCR of STRADα and STRADβ across developmental time. (D) Reverse transcriptase-PCR (RT-PCR) of STRADα indicates that multiple variants exist in distinct tissue types. In particular, the largest species (arrowhead) appears to be specific to brain, skeletal muscle and testes. (E) RT-PCR products from enriched cultures of the dominant CNS cell types. (STRADα-1 isoform – arrowhead; STRADα-4 isoform - asterisk). Cort neurons – cerebral cortex primary neurons; Interneurons – medial ganglionic eminence primary neurons, Astrocytes – primary post-natal day 1 astrocytes, Oligo – primary oligodendrocyte cultures. (F) RT-PCR of STRADα isoforms across developmental time in the cerebal cortex. CNS, central nervous system.
Mentions: The vast networks of neural projections in the brain are essential for appropriate connectivity, but how these axons are specified during neuronal differentiation remains unclear. The regulatory mechanisms coordinating axon formation are only beginning to emerge despite the identification of key signaling molecules [1-3]. The protein kinase Liver Kinase B1 (LKB1) is a requisite component of the transduction machinery controlling axon specification both in vitro and in vivo [4,5]. LKB1 catalytic activity is allosterically regulated by the related pseudokinases, STRAD (STe20 Related ADapter)-alpha and STRAD-beta (STRADα and STRADβ) (Figure 1A, [6,7]). While little is known about STRADβ function, homozygous deletion within the human LYK5 (STRADα) locus (see Additional file 1: Figure S3A) results in a syndromic condition known as polyhydramnios, megalencephaly, and symptomatic epilepsy (PMSE) [8]. These patients have craniofacial dysmorphology, cognitive deficits, and intractable infantile-onset epilepsy. Given the clear impact on human health and brain development, further insights into STRAD pseudokinases are needed to clarify their contributions to nervous system development and disease.

Bottom Line: We find that STRADα is highly spliced and appears to be the primal STRAD paralog.We also reveal a reciprocal protein-stabilizing relationship in vivo between LKB1 and STRADα, whereby STRADα specifically maintains LKB1 protein levels via cytoplasmic compartmentalization.We demonstrate a novel role for STRADβ in axogenesis and also show for the first time in vivo that STRADα, but not STRADβ, is responsible for LKB1 protein stability.

View Article: PubMed Central - HTML - PubMed

Affiliation: Department of Pediatrics-Doernbecher, Children's Hospital, Portland, OR 97239, USA. barnesan@ohsu.edu.

ABSTRACT

Background: Neuronal polarization is an essential step of morphogenesis and connectivity in the developing brain. The serine/threonine kinase LKB1 is a key regulator of cell polarity, metabolism, tumorigenesis, and is required for axon formation. It is allosterically regulated by two related and evolutionarily conserved pseudokinases, STe20-Related ADapters (STRADs) α and β. The roles of STRADα and STRADβ in the developing nervous system are not fully defined, nor is it known whether they serve distinct functions.

Results: We find that STRADα is highly spliced and appears to be the primal STRAD paralog. We report that each STRAD is sufficient for axogenesis and promoting cell survival in the developing cortex. We also reveal a reciprocal protein-stabilizing relationship in vivo between LKB1 and STRADα, whereby STRADα specifically maintains LKB1 protein levels via cytoplasmic compartmentalization.

Conclusions: We demonstrate a novel role for STRADβ in axogenesis and also show for the first time in vivo that STRADα, but not STRADβ, is responsible for LKB1 protein stability.

Show MeSH
Related in: MedlinePlus