HYPOTHESIS : WHERE DO CYCLINS COME FROM?

There is increasing evidence that Cyclins are integrins and so are Tumor growth factors, Tumor Necrosis factors, interleukins and interferons.
All these are membrane proteins with a particularity to be released from Metalloprotease and related adhesion molecules depending on the nature of stimuli.  The discovery and description of ADAMs as type I membrane protein containing Metalloproteinase and an integrin domain locate the growth factors and Cyclins squarely at the membrane  (surface and reticulum membrane).  These proteins, once released, go straight to the Nucleus to unveil their might by activating transcription factor.  In their track to the nucleus they can amplify and activate signal transduction pathways as well as either molecules. The cyclins find cytoplasmic and protein substrates (mostly enzymes)  which have their specific domains and link to the site to activate them most of the time, changing their shapes so as to expose hidden electrons or atomic groups (such SH) to cause downstream chain activation.

Now as the pathway unfolds at light speed (or electronic speed) it may overwhelm the cell, protection has to be assured to hide death domains (which also are integrins and therefore at the membrane) and pathways to Apoptosis.  Protection at the membrane seems to be offered by the INK while the CIP/Kip.  But deep in the cell are the Bcl-like proteins. The CIP/Kip seems to work like Decoy specific proteins since the have Cyclin domain to stop them from stimulating their respective CDKs (Cyclin dependent Kinases).  Some CDKs need 2 or more different stimulations to accomplish their deed. And with the number of stimulations comes the consequent activation of various substrates.  The Retinoblastoma substrate governs the G1 progression phase in the cell cycle, but it needs at least 2 activations, first by Cyclin D followed by activation by Cyclin E in order for it to free E2F that light up tarnscrptions genes which control the path to S-phase.  This Cyclin E also activates processes leading to Histone Biosynthesis, Centrosome activity and DNA replication.  And in fact, Cyclin E is the one that leads to gene instability that characterize many triple negative breast cancers

(E2F AND CYCLIN E, ARE POWERFUL TARGETS FOR CANCER CURE)

One of the CIP/Kip(s) is the P21 which plays a role in the cell cycle arrest due to P53 activation.
I should note that the Kinase itself may be mutated.  CDK4 is mutated in Melanoma, it renders the INK4 protein unable to occupy its domain and therefore is free to affect the nuclear transcription factor.  Therefore the solution is to increase the ligand to INK4 so as to increase its ubiquitination and and degradation through the proteasome (Ipilimumab/CTLA 4 in T cell/ does not do this unfortunately, so there is more room for you to research).  YES, LIKE FOR MERCEDES, WE NEED THE E CLASS OF PROTEINS TO FURTHER UBIQUITINATION.  A MUTATION IN E CLASS (WHICH INCLUDES MDM2) WILL BE BAD IN MELANOMA!

Suffice is to show that what starts at the membrane moves quickly to the nucleus in a milli-milli second in a flash and turn the life of the host around!

It is worth noting that not only Cyclins can be blocked from entering the Nucleus where they trigger transcription factor formation, but sometimes the Decoy (Cip/Kip) is stopped from entering the nucleus and cannot stop Cyclins which have entered the nucleus: this happens in breast cancer (p27 mislocation)
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THE INTEGRINS, PRESUMED SOURCE OF CYCLINS!