pkb*

Oncogenes and tumour suppressors are mutation targets promoting the onset and maintenance of cancer. Oncogenic mutations result in gain-of-function and deregulation of the function of the oncoprotein that they encode. Tumour suppressors act to run quality checking of DNA, keep cell cycle checkpoints, and shut down mitogenic signals; mutations in genes encoding tumour suppressors can lead to absence of these checks and give activated oncoproteins the chance to run riot in a cell. Co-incidence of mutations in oncogenes and tumour suppressor genes potentially leads to cancer.

Oncogenes

Ras is a small G protein involved in a whole host of cellular functions. Mutation of Ras at a functional site can lead to a pleiotropic phenotype. Oncogenic Ras causes inappropriate signalling through its three pathways: MAPK, PI3K, and RalGEF. Signalling through the PI3K activates antiapoptotic Akt (PKB), which acts to promote cell survival. Signalling through RalGEF causes cell motility by formation of filopodia (Cdc42) and lamellipodia (Rac), which may be associated with metastasis. Signalling through MAPK actually causes the expression of some Ras signalling inhibitors (Sproutys, SPREDs, GAPs) which shuts down the signal in normal cells.

Myc is a transcription factor with more than 8000 transcription targets. Deregulated Myc leads to cell proliferation, but does not block apoptosis. Thus, it leads to a modest amount of growth before it is eradicated by apoptosis. Inhibition of apoptosis by antiapoptotic Bcl-xL is tumourigenic in cells expressing Myc highly. Additionally, Myc is thought to contribute to the tumour microenvironment, immune evasion, and inhibition of differentiation.

Ras and Myc work together by combining their abilities. Myc promotes cell proliferation and disfavours differentiation, and Ras inhibits apoptosis. The combination of the two means that cells are allowed to proliferate without triggering apoptosis. Ras actually activates Myc in normal cells - but in normal cells, activation is transient. Ras stabilises Myc by phosphorylation on S62 through MEK signalling, but also promotes its degradation by phosphorylation on T58 through PI3K signalling. The result is transient activation of Myc by Ras. Mutations which ultimately block phosphorylation at T58 will switch activation by Ras from a transient to a constitutive response.

Tumour suppressors

p53 is the so-called guardian of the genome. High Myc and oncogenic Ras cause stabilisation and activation of p53. p53 gets two bites at the cherry to combat the inheritance of damaged genomes: at the point of DNA damage, p53 arrests the cell until the DNA is repaired. p53 decides whether the cell enters senescence or apoptosis - its own state of post-translational modifications and the genomic context of its target genes (p53 is also a TF) on the genome in that particular cell both play a role in which way the scale tips. In this way, p53’s second bite of the cherry is the selection of apoptosis in cells whose DNA is damaged beyond repair.

Rb is the keeper of the G1/S checkpoint. Loss of both copies of the Rb gene leads to retinoblastoma. Familial retinoblastoma predisposes heterozygotes with a heightened risk of retinoblastoma by loss of heterozygosity - loss of their only functional copy. This can occur by mutation, but also by mitotic recombination, gene conversion, and nondisjunction. Cells null for Rb can still enter G0 phase, as p107 and p130 share some redundant functions with Rb.

NF1 displays the phenomenon of haploinsufficiency. Nf1-/- Schwann cells can be complemented for the wild-type by Nf1+/+ mast cells, but not Nf1+/- mast cells. The former gives the wild-type; the latter causes neurofibromas.

VHL suppresses the hypoxic response in normoxia by mediating the ubiquitin-associated degradation of HIF-1α in normoxia. Loss of VHL leads to a hypoxic response no matter the oxygen level.

Further reading:

  • Hanahan, D.; Weinberg, R.A. 2011. “Hallmarks of cancer: The next generation.” Cell 144:646-674.
  • Lowe, S.W.; Cepero, E.; Evan, G. 2004. “Intrinsic tumour suppression.” Nature 432:307-315.
  • Pylayeva-Gupta, Y.; Grabocka, E.; Bar-Sagi, D. 2011. “RAS oncogenes: Weaving a tumorigenic web.” Nature Reviews Cancer 11:761-774.
  • Soucek, L.; Evan, G.I. 2010. “The ups and downs of Myc biology.” Current Opinion in Genetics and Development 20:91-95.
  • Vousden, K.H.; Prives, C.; 2009. “Blinded by the light: The growing complexity of p53.” Cell 137:413-431.
  • Burkhart, D.L.; Sage, J. 2008. “Cellular mechanisms of tumour suppression by the retinoblastoma gene.” Nature Reviews Cancer 8:671-682.
Kiedyś zrobię porządek, ze wszystkim. Poukładam chaos w głowie, zacznę się zdrowo odżywiać, wreszcie zrobię remont, zmienię pracę, środowisko, miejsce zamieszkania, stan cywilny i procent pkb. Kiedyś się ustatkuję i przestanę przejeżdżać na pomarańczowym i pić herbatę z cytryną, bo to wywołuje alzheimera. Przestanę być wiecznie niepoważna i dziecinna, bo kto to widział, mając tyle lat co ja. W sumie, zacznę też inaczej patrzeć na to wszystko, może pogodzę się z matką i zacznę chodzić do kościoła i kupię wreszcie regał, bo kto to widział, układać sterty książek na podłodze.
Ale nie dzisiaj. Dziś lekką ręką wydałam *wolęniemyślećile* na ciepłe ubrania, bo w styczniu biorę urlop i jadę w Karkonosze. W końcu nie wiem kiedy nastąpi kiedyś i wolę do tego czasu jeszcze pożyć, zanim zwariuję do reszty.
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Evening Quickie #soldierporn: Far from home.

Sailors assigned to Commander, Task Group 56.7 pass Prince Khalifah Bin Salman Causeway in a riverine command boat during a training exercise. CTG-56.7 provides a multi-mission platform for the U.S. 5th Fleet area of responsibility by focusing on maritime security operations, maritime infrastructure protection, and theater security cooperation efforts, in addition to offensive combat operations.

(U.S. Navy photos by Mass Communication Specialist 1st Class Michelle L. Turner, 6 JAN 2014.)

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Methylamine CH5N

  • Appearance: Colorless gas
  • Molar Mass: 31.06 g/mol
  • density: 694 kg/m3
  • Melting Point: -93.10 °C
  • Boiling Point: -6.6°C 
  • pKb: 3.36

Methylamine is a derivative of ammonia and is the simplest primary amine. It’s commonly sold as anhydrous gas in metal containers. It’s a relatively easy compound to synthesis in lab, being a simple reaction between methanol and ammonia. Methylamine is a great nucleophile that’s also highly basic with little to no hindrance. Liquid methylamine has solvent properties similar to ammonia. It is toxic and listed as a List 1 Precursor chemical by the DEA since it’s well known for it’s use in the production of methamphetamine.