The Small Guys That Help Regulate Protein Synthesis

If you have an interest in cellular biology, the chances are you've come across the different types of nucleic acids that are used to code for proteins and control certain activities of the cell. However, what might be new to you is the existence of MicroRNA or miRNA, in its common notation. Essentially these are regular strands of RNA but very small - in fact a regular sized RNA molecule may be around 100 times longer than the average length miRNA. As miRNA are single stranded, the molecules tend to quite flexible, in contrast to the well known rigid DNA double helix molecule. Originally, scientists tended to believe that in eukaryotic cells at least, there were only two types of RNA: ribosomal RNA and messenger RNA. At first, miRNA were seen to be RNA that were too insignificant to have any real function, they were considered free clumps of nucleotides in short.

Now the importance of miRNA molecules has been realised, thanks to cutting edge research on a particular type of nematode worm - specifically Caenorhabditis elegans. In 1993, the first miRNA identified was named lin-4. What scientists found is that somehow, these minute molecules prevent the development of the larvae. 

After these baby steps into this field of research, the year 2000 saw the discovery of the miRNA molecule let-7. This was found to 'regulate development in C.elegans'. What was more significant however, was that this molecule could be found in all animal and plant cells. But what do we mean by 'regulate development'? This particular miRNA molecule is found to be responsible for controlling aspects of the cell cycle and cell differentiation. But healthy functioning cells doesn't rely on a single miRNA molecule - many different molecules working together ensure cellular processes go on as intended.

But how do miRNA's work?

In an average human cell, over 1000 different miRNA molecules can be found. Each of these specific strands seek to target a particular RNA molecule. With over 60% of RNA molecules being targeted by miRNAs, it could be said that controlling protein synthesis is a very organised and vast operation. What is important to note, is that miRNA molecules are encoded by genes, a lot like proteins in fact. It follows that these genes are present in the cell's DNA.

To synthesise miRNA, firstly one long strand of specially structured RNA is manufactured from miRNA genes. These could be considered the precursors of miRNA (Pri-miRNA) and are subsequently lysed by enzymes and transported from the nucleus, into the cytoplasm. Any two different  miRNAs can align through regular RNA-RNA hydrogen bonded base-pairing. However in some parts, there may be some non-complementary base pairing which would lead to bulges from the molecule. Using specific enzymes, the hydrogen bonds can be broken to leave two separate miRNA molecules which can go on to target their designated RNA molecule.

Due to inconsistencies in base pairing with an mRNA molecule, miRNAs have been found to inhibit protein synthesis by preventing the ribosome translating the RNA molecule. But another way miRNA's function is that they can achieve complete complementary base pairing with an mRNA molecule. Specific degrading enzymes can then recognise this situation and destroy the miRNA-mRNA complex, preventing the protein ever being synthesised.

(Two examples of pri-miRNA - sequences in red represent 'mature' miRNA. Notice there are bulges where there is no complementary base pairing - WIkipedia - microRNA)

Extended research has shown that 'malfunction of miRNAs is implicated in some liver diseases, diseases of the nervous system, cardiovascular disease, cancer and obesity'. One example given in the September issue of the Biological Sciences Review is miRNAs affecting normal nervous function. Individuals with mental retardation sometimes have whats called "fragile X syndrome", where as implied, the X chromosome tends to break easily. In association with this, it has been found that in the nerve cells of these individuals, miRNA molecules have prevented the synthesis of an essential protein by binding with mRNA.

Even miRNA has been believed to be the culprit in some cancers. It isn't always bad that an miRNA molecule binds to RNA - some miRNAs suppress tumour growth whilst others promote it.

At present, it may be difficult to see how miRNAs can be used to treat disease, but I believe there is no doubt that it could one day be widely use to diagnose them. Cancers are a good example. It has been observed that particular concentrations of a miRNA can correlate with different rates of growth of malignant tumours. From miRNA analysis, it may be possible for doctors to predict the best treatment options for patients.

However this does't mean treatment isn't possible! According to Professor Sheila Graham of the University of Glasgow, new research has revealed the potential of "miRNA sponges" in cells. These are non-functioning RNA molecules that "mop up" specific miRNA molecules so that they can't interrupt the synthesis of essential proteins.



Credit to Professor Sheila Graham for her article 'MicroRNAs - small players in big diseases' published in the Biological Sciences Review (Volume 27, Number 1).

Treating Brain Tumours With Proton Beam Therapy

What has been highlighting the news recently is the Ashya King case and the implications of certain therapies to treat brain tumours. Ashya King is the five year old son of parents Brett and Naghemeh King. Whilst Ashya was being treated in a UK hospital, his parents, without consent from doctors, took him from hospital and journeyed overseas to seek the treatment they wanted for their son. Mr and Mrs King were in preference for proton beam therapy for their son - this directly targets cancer cells and is considered to have less side effects than the conventional radiation/X-ray therapy. However currently in the UK, proton beam therapy isn't available for the treatment of tumours like Ashya has -  instead it has only been used to treat certain eye conditions. Government legislation says that proton beam therapy will be introduced in combating cancers like Ashya has by 2018. Understandably, Ashya's parents simply cannot wait that long for the treatment; it is important to intervene as early as possible when tackling a tumour as severe's as Ashya's.

What is proton beam therapy?

X-rays have long been used to treat cancerous tumours. Given in sufficiently high doses, X-rays will be able to kill tumour cells, however what many people view as a fundamental flaw is that healthy tissues can be exposed to similar intensity radiation. This leaves risk of healthily tissue being destroyed which can in turn be potentially detrimental to health. Therefore many people believe proton beam therapy to be the best option, as even in high concentrations there is greatly reduced damage to healthy tissues (and more importantly, the vital organs). The problem that arises is that those receiving X-ray therapy will receive a lesser dose than desired by doctors as the risk to healthy tissue comprises the treatment. Many patients desire proton beam therapy partly because of this.

Recalling fundamental chemistry, protons are subatomic particles of the atom which are positively charged. They have a relative charge of +1. Opposing this, 'orbiting' electrons have a relative charge of -1, and thus the two subatomic particles have an attraction for each other. Having this rather basic intuition allows us to make sense of how proton beam therapy works. As charged particles, such as protons are fired near other molecules or atoms, they become attracted to the elections with orbit the atoms. This causes the atoms to ultimately lose electrons and as a result become positively charged. These are now ions. Obviously, this process is therefore called ionisation which causes the chemical properties of that atom to change. This is vitally important when targeting cancer cells. As the proton beam targets the cells, the molecules within those cells become damaged, or ionised. However it matters what molecules become affected, for example to damage the DNA of a cancer cell means destroying it's functionality. As a result, key processes such as mitosis (cellular division) and DNA replication become disrupted. With a high enough dosage, no matter how hard enzymes work to repair the damage, their efforts become futile. Cancer cells have less capability of repairing damage to organelles and molecules than healthy cells, which means minimal concern for the normal cells that are bombarded with the proton beam. Fundamentally, the proton beam creates a selection pressure on cancer cells, they are more likely to be destroyed and subsequently their numbers decline. 

Although both X-rays and proton beams aim to target cancer cells, it is considered that the precision and accuracy of the proton beam is greater. The 'distribution of protons can be directed and deposited in tissue volumes'. Another downfall with X-rays is that as they 'lack charge and mass', their use results in radiation being deposited 'in normal tissues near the body's surface'. This ultimately poses a risk of genetic mutation to healthy cells.

Interestingly, protons can be accelerated or decelerated as and when required - X-rays cannot be 'energised to specific velocities' unlike protons. This property of protons allows physicians to have some element of control as to how penetrative the proton beam is. As a very physical entity, protons slow down as they penetrate further into tissue, coming into contact with more electrons as a result. It follows that as the protons decelerate, they eventually stop at their designated site - the cancer cells. This is not the case with X-rays as some radiation is left to pass through the tumour tissue and through to other healthy tissue via an "exit dose" before exiting the patient completely.

I have empathy as to why the parents of Ashya want to pursue this proton beam therapy. With fewer side effects and less damage to normal tissue, it is highly likely that Ashya would enjoy 'a better quality of life during and after proton treatment'.


Credit to the BBC on their updates on the Ashya King case and to The National Association for Proton Therapy for their article 'How Proton Treatment Works'. Read more on the subject here.

Image: Patient receiving radiation therapy - BBC

The Potential of Recombinant Proteins to Treat Disease

An article in the Biological Sciences Review (Volume 23, Number 4) grabbed my attention today, although it was published in April 2014. Nonetheless I feel it is very relevant. It was about how recombinant proteins can be used to treat certain chronic diseases, rheumatoid arthritis and multiple sclerosis are just a named couple.

I don't feel I should need to go into all the theory about protein synthesis, but in case you weren't sure, below is a very useful visual intuition:



Recombinant proteins are synthesised by manipulating the cell and almost 'tricking' the cell to making the desired proteins we require. Usually this is achieved by introducing some (foreign) DNA into the cell which codes for the functional protein, then the normal 'protein expression' is able to follow using ribosomes. One example of this would be insulin protein being synthesised by bacteria by using it's plasmid as a vector. One thing to note is that if mammalian cells and bacterial cells were to be used, the protein product many not necessarily be identical as the protein folding procedure may slightly differ for eukaryotic and prokaryotic cells.

Examples of recombinant proteins include insulin as mentioned and therapeutic antibodies.

What I find very exciting is that these antibodies are able to target specific cells - you may have heard of monoclonal antibodies under the same context. This could mean the targeting of cancer cells, as cancer cells have a unique antigen on their plasmalemma. Therefore therapeutic antibodies can be engineered to target these cells. The formation of an antigen-antibody complex can result in a number of consequences: inhibition of growth, immobilisation (pathogenic cells) and detoxification.


One interesting idea from the article explains how using therapeutic antibodies may help to lessen the pain for individuals with chronic diseases such as arthritis, by inhibiting the activity of certain ion channels in nerve cells.

Ion channels are transmembrane (intergal) proteins that allow passage of ions from one cell to another - pain signals are achieved in this way. Some rare individuals have equally the rare inability to feel pain. This condition was explained by scientists who saw that there was a rare mutation in the gene SCN9A (this gene codes for the synthesis of these ion channels). Therefore using this fascinating occurrence there is the potential of using specific therapeutic antibodies to target these particular ion channels. The result of this will inevitably be a reduction in the number of functioning ion channels.

I appreciate that this technique may not cure the disease for good, but this would be a major breakthrough in pain management for chronic diseases. These conditions have dramatic effects on an individuals quality of life, so lessening the pain can improve their mental health.


It would be a major achievement to get this treatment underway. However like with any drug rigorous testing over many stages must be carried out first.

I look forward to seeing the progress of this idea in the future…

Credit to Katharine Cain, postdoctoral scientist at UCB pharmaceutical company, for the original article.