Updated: 2/12/2018

Intermediate Filaments

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Overview

Structure
- stable polymers
  - unlike microtubules and actin → does not undergo dynamic treadmilling
  - must be degraded via the ubiquitin pathway
    
    sends to proteasomes
- intermediate in size between microfilaments (7 nm) and microtubules (25 nm)

Function
- give strength to the cytoskeleton
- 5 types

                        TypeFilament nameLocationsStain
I-IIKeratinEpithelial cellsCytokeratin
IIIDesminMuscle (smooth, cardiac, and skeletal)Desmin
PeripherinPeripheral nerve axons -
VimentinFibroblasts and endotheliumVimentin
Glial fibrillary acidic protein (GFAP)Astrocytes and Schawnn cellsGFAP
IVNeurofilamentsNeuronsNeurofilament (NF)
VLaminsNuclear envelope of all cells-

                    
                    
                    
                

Type	Filament name	Locations	Stain
I-II	Keratin	Epithelial cells	Cytokeratin
III	Desmin	Muscle (smooth, cardiac, and skeletal)	Desmin
	Peripherin	Peripheral nerve axons	-
	Vimentin	Fibroblasts and endothelium	Vimentin
	Glial fibrillary acidic protein (GFAP)	Astrocytes and Schawnn cells	GFAP
IV	Neurofilaments	Neurons	Neurofilament (NF)
V	Lamins	Nuclear envelope of all cells	-

Clinical importance
- alcoholic liver disease
  - ubiquitinated cytokeratin filaments accumulate in hepatocytes
    
    eosinophilic inclusions called Mallory bodies
- Parkinson's disease
  - alpha-synuclein and ubiquitinated neurofilaments accumulate in neurons of substantia nigra
  - eosinophilic inclusions called Lewy bodies

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40%	2	H
60%	3	F	Enter (backside only)
80%	4	E
100%	5	M
Toss	0	T

Questions (1)

(M1.BC.17.4753) A 55-year-old female presents to her primary care physician complaining of a mass in her mid-thigh. The mass has grown slowly over the past six months and is not painful. The patient’s past medical history is notable for hypertension and hyperlipidemia. She takes lisinopril and rosuvastatin. On examination, there is a firm, immobile mass on the medial aspect of the distal thigh. She has full range of motion and strength in her lower extremities and patellar reflexes are 2+ bilaterally. A biopsy of the mass reveals multiple pleomorphic smooth muscle cells with nuclear atypia. The patient subsequently initiates radiation therapy with plans to undergo surgical resection. This tumor will most strongly stain for which of the following?

QID: 108852

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Chromogranin

13%

(28/216)

Desmin

57%

(124/216)

Cytokeratin

12%

(26/216)

Glial fibrillary acidic protein

(8/216)

Neurofilament

(12/216)

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