Converting Map Projection meters to decimal degrees

[Ryan Ollerenshaw]

I am using  NASA's ISIS software to get data from their Planetary Data 
System.  I have already created a base map using the Proj4 projection 
4326.  But i am not sure how to convert an ISIS simpleCylindrical 
projection (units in meters) to a Proj4 projection (units in decimal 
degrees).

Thanks,
-Ryan

Proj4:
<4326> +proj=longlat +ellps=WGS84 +datum=WGS84 +no_defs  <>

ISIS:
Group = Mapping
  ProjectionName         = SimpleCylindrical
  TargetName             = Mars
  EquatorialRadius       = 3396190.0 <meters>
  PolarRadius            = 3376200.0 <meters>
  LatitudeType           = Planetocentric
  LongitudeDirection     = PositiveEast
  LongitudeDomain        = 360
  MinimumLatitude        = -1.3695743239693
  MaximumLatitude        = -1.0943032756341
  MinimumLongitude       = 356.0083751075
  MaximumLongitude       = 356.09326944036
  PixelResolution        = 4.3931469117577 <meters/pixel>
  CenterLongitude        = 356.05082227393
  Scale                  = 13492.537061455 <pixels/degree>
  TrueScaleLatitude      = 0.0
  UpperLeftCornerX       = -2517.2731804372 <meters>
  UpperLeftCornerY       = -64860.421005191 <meters>
  LineProjectionOffset   = 14764.5
  SampleProjectionOffset = -572.5
End_Group
End